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http://www.wiki.mkrd.info/index.php?title=Programmable_Logic_Devices&diff=1454
Programmable Logic Devices
2015-10-17T20:11:20Z
<p>Mkrdwiki: /* SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available */</p>
<hr />
<div>This page will cover simple PLD devices useable for hobby, prototyping, and similar applications. Costs are for quantity of 1 (one). Some devices (like Lattice Semiconductor MachXO3 FPGA's) are available as BGA package only. As available from Digi-Key. Last parsing 5Sept14. <br />
<br />
Most manufacturers are discontinuing production of PLDs, with the attention going to FPGAs, CPLDs, ASICs, and microprocessors / microcontrollers.<br />
<br />
<br />
The following are the remaining devices which are still being manufactured and are not under EOL (End of Life) / Discontinued notices. <br />
<br />
<br />
== PLDs (PAL, PLA, GAL, SPLD): ==<br />
<br />
* '''Atmel'''<br />
** '''ATF Family'''<br />
<br />
[http://www.atmel.com/products/Other/spld-cpld/spld-industry_standard.aspx]<br />
<br />
<br />
* '''Texas Instruments'''<br />
** '''PAL Family'''<br />
** '''TIBPAL Family'''<br />
** '''TICPAL Family'''<br />
<br />
[http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?familyId=317&family=logic&uiTemplateId=SZVI_T]<br />
<br />
<br />
== Cheap CPLDs - LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Atmel'''<br />
** '''ATF15xx'''. [http://www.atmel.com/products/Other/spld-cpld/cpld_atf15xx_family-industry_standard_compatible.aspx]<br />
** '''ATF750'''. [http://www.atmel.com/products/Other/spld-cpld/cpld-2_22v10s_in_24-pin_and_28-pin_packages.aspx]<br />
** '''ATF2500C'''. [http://www.atmel.com/devices/ATF2500C.aspx]<br />
<br />
<br />
* '''Altera Corporation'''<br />
** '''MAX 3000A Family'''<br />
** '''MAX 7000 Family'''<br />
** '''MAX Family'''<br />
** '''MAX II Family'''<br />
** '''MAX V Family'''<br />
[http://www.altera.com/devices/cpld/cpld-index.html]<br />
<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''ispMACH''' series<br />
** '''ispMACH 4000''' series<br />
** '''ispMACH 4A''' series<br />
** '''ispLSI 2000''' series<br />
** '''ispLSI 1000''' series<br />
[http://www.latticesemi.com/products/cpld/index.cfm]<br />
<br />
<br />
* '''Xilinx Inc'''<br />
** '''CoolRunner II'''<br />
** <strike>'''CoolRunner XPLA3'''</strike>. Mature (not for new designs) / discontinued.<br />
** '''XC9500XL'''<br />
[http://www.xilinx.com/products/silicon-devices/cpld/index.htm]<br />
<br />
== SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''iCE40 Family'''. LM, LP, HX. Tiny device, oriented for very low power, very small size, and mobile applications. Almost all package offerings are BGA. '''LM in BGA packages only (not for prototyping, hobbyist, student, low-volume).''' LP / HX two SMD packages (VQFP, TQFP) available.<br />
** '''iCE40 Family'''. Ultra / UltraLite. Tiny device, oriented for very low power, very small size, and mobile applications. The iCE40 UltraLite is available in BGA or FN (Flat, No Leads – generally not hand solderable) packages only. The iCE40 UltraLite is available in BGA packages only. Programmed with the iCEcube2 Design Software only (not Lattice Diamond). VCCIO 3.3V or less. '''Not for prototyping, hobbyist, student, low-volume.'''<br />
** '''MachXO Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip.<br />
** '''MachXO2 Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip. VCCIO 3.3V or less.<br />
** '''MachXO3 Family'''. Low power, instant-on, non-volatile FPGA. '''BGA packages only (not for prototyping, hobbyist, student, low-volume)'''. VCCIO 3.3V or less. More expensive LF devices use on-board flash. Cheaper L devices use proprietary NVCM (details are sketchy, refer to http://www.latticesemi.com/~/media/LatticeSemi/Documents/WhitePapers/HM/MultitimeProgrammableULDFPGAs.pdf?document_id=50424). NVCM seems to be rewriteable a much smaller number of times than Flash, but claims to result in smaller, cheaper, and lower-power devices. <br />
** <strike>'''LatticeECP & EC Families'''</strike>. Mature (not for new designs).<br />
[http://www.latticesemi.com/products/fpga/index.cfm?source=topnav]<br />
<br />
Royalty-free LatticeMico8 8-bit microprocessor soft core available for MachXO2 devices.<br />
<br />
<br />
* '''Microsemi SoC (Actel)'''<br />
** '''ProASIC3 nano'''. Non-volatile.<br />
** '''ProASIC3'''. Non-volatile.<br />
** '''IGLOO'''. Non-volatile.<br />
** '''IGLOO nano'''. Non-volatile.<br />
[http://www.actel.com/products/devices.aspx]<br />
<br />
Royalty-free ARM Cortex-M1 32-bit microprocessor soft core available<br />
<br />
<br />
* '''Xilinx'''<br />
** <strike>'''Spartan'''</strike>. Mature (not for new designs) / discontinued. <br />
** <strike>'''Spartan-II'''</strike>. Mature (not for new designs) / discontinued. <br />
** '''Spartan-3A'''. Volatile. <br />
** '''Spartan-3AN'''. Non-volatile.<br />
<br />
Soft-cores 8-bit PicoBlaze Controller and 32-bit MicroBlaze Processor are available.<br />
<br />
== Programmers, Evaluation boards, and Software ==<br />
<br />
The devices are worth not very much, it is the support you get what matters. Instead of comparing devices, what needs to be compared are the software, development tools, community, and available support.<br />
<br />
<br />
* '''Atmel'''. Win-CUPL Design Software is provided for free. An ATF15XX-DK3 CPLD Development/Programmer Kit is available. ProChip Designer V5.0 is a pro design suite. ''Eval boards?''. Note: the software and the kit seem to be a bit dated (Windows XP is specified, etc).<br />
* '''Texas Instruments'''. No software, programmers, or evaluation kits are available from TI, but generic PAL programmers can be used.<br />
* '''Altera Corporation'''. Several development kits are available. Some, however, are from third-party sources. Devices seem to need a lot of other devices for support on the eval boards.<br />
* '''Lattice Semiconductor Corporation'''. Plenty of evaluation boards, breakout boards, etc are avalable. All eval boards and software are up to date.<br />
* '''Xilinx Inc'''. For $59, a CoolRunner-II CPLD Starter Kit is available with an evaluation board, programmer, software, and plenty of documentation.<br />
* '''Microsemi SoC (Actel)'''. For $99 you get the Starter Kit with an evaluation board, programmer, software, and documentation.</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Programmable_Logic_Devices&diff=1453
Programmable Logic Devices
2015-10-17T20:03:00Z
<p>Mkrdwiki: /* SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available */</p>
<hr />
<div>This page will cover simple PLD devices useable for hobby, prototyping, and similar applications. Costs are for quantity of 1 (one). Some devices (like Lattice Semiconductor MachXO3 FPGA's) are available as BGA package only. As available from Digi-Key. Last parsing 5Sept14. <br />
<br />
Most manufacturers are discontinuing production of PLDs, with the attention going to FPGAs, CPLDs, ASICs, and microprocessors / microcontrollers.<br />
<br />
<br />
The following are the remaining devices which are still being manufactured and are not under EOL (End of Life) / Discontinued notices. <br />
<br />
<br />
== PLDs (PAL, PLA, GAL, SPLD): ==<br />
<br />
* '''Atmel'''<br />
** '''ATF Family'''<br />
<br />
[http://www.atmel.com/products/Other/spld-cpld/spld-industry_standard.aspx]<br />
<br />
<br />
* '''Texas Instruments'''<br />
** '''PAL Family'''<br />
** '''TIBPAL Family'''<br />
** '''TICPAL Family'''<br />
<br />
[http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?familyId=317&family=logic&uiTemplateId=SZVI_T]<br />
<br />
<br />
== Cheap CPLDs - LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Atmel'''<br />
** '''ATF15xx'''. [http://www.atmel.com/products/Other/spld-cpld/cpld_atf15xx_family-industry_standard_compatible.aspx]<br />
** '''ATF750'''. [http://www.atmel.com/products/Other/spld-cpld/cpld-2_22v10s_in_24-pin_and_28-pin_packages.aspx]<br />
** '''ATF2500C'''. [http://www.atmel.com/devices/ATF2500C.aspx]<br />
<br />
<br />
* '''Altera Corporation'''<br />
** '''MAX 3000A Family'''<br />
** '''MAX 7000 Family'''<br />
** '''MAX Family'''<br />
** '''MAX II Family'''<br />
** '''MAX V Family'''<br />
[http://www.altera.com/devices/cpld/cpld-index.html]<br />
<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''ispMACH''' series<br />
** '''ispMACH 4000''' series<br />
** '''ispMACH 4A''' series<br />
** '''ispLSI 2000''' series<br />
** '''ispLSI 1000''' series<br />
[http://www.latticesemi.com/products/cpld/index.cfm]<br />
<br />
<br />
* '''Xilinx Inc'''<br />
** '''CoolRunner II'''<br />
** <strike>'''CoolRunner XPLA3'''</strike>. Mature (not for new designs) / discontinued.<br />
** '''XC9500XL'''<br />
[http://www.xilinx.com/products/silicon-devices/cpld/index.htm]<br />
<br />
== SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''iCE40 Family'''. LM, LP, HX. Tiny device, oriented for very low power, very small size, and mobile applications. Almost all package offerings are BGA. '''LM in BGA packages only (not for prototyping, hobbyist, student, low-volume).''' LP / HX two SMD packages (VQFP, TQFP) available.<br />
** '''iCE40 Family'''. Ultra / UltraLite. Tiny device, oriented for very low power, very small size, and mobile applications. The iCE40 UltraLite is available in BGA or FN (Flat, No Leads – generally not hand solderable) packages only. The iCE40 UltraLite is available in BGA packages only. Programmed with the iCEcube2 Design Software only (not Lattice Diamond). VCCIO 3.3V or less. '''Not for prototyping, hobbyist, student, low-volume.'''<br />
** '''MachXO Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip.<br />
** '''MachXO2 Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip. VCCIO 3.3V or less.<br />
** '''MachXO3 Family'''. Low power, instant-on, non-volatile FPGA. '''BGA packages only (not for prototyping, hobbyist, student, low-volume)'''. VCCIO 3.3V or less. LF devices use on-board flash. L devices use proprietary NVCM (details are sketchy, refer to http://www.latticesemi.com/~/media/LatticeSemi/Documents/WhitePapers/HM/MultitimeProgrammableULDFPGAs.pdf?document_id=50424)<br />
** <strike>'''LatticeECP & EC Families'''</strike>. Mature (not for new designs).<br />
[http://www.latticesemi.com/products/fpga/index.cfm?source=topnav]<br />
<br />
Royalty-free LatticeMico8 8-bit microprocessor soft core available for MachXO2 devices.<br />
<br />
<br />
* '''Microsemi SoC (Actel)'''<br />
** '''ProASIC3 nano'''. Non-volatile.<br />
** '''ProASIC3'''. Non-volatile.<br />
** '''IGLOO'''. Non-volatile.<br />
** '''IGLOO nano'''. Non-volatile.<br />
[http://www.actel.com/products/devices.aspx]<br />
<br />
Royalty-free ARM Cortex-M1 32-bit microprocessor soft core available<br />
<br />
<br />
* '''Xilinx'''<br />
** <strike>'''Spartan'''</strike>. Mature (not for new designs) / discontinued. <br />
** <strike>'''Spartan-II'''</strike>. Mature (not for new designs) / discontinued. <br />
** '''Spartan-3A'''. Volatile. <br />
** '''Spartan-3AN'''. Non-volatile.<br />
<br />
Soft-cores 8-bit PicoBlaze Controller and 32-bit MicroBlaze Processor are available.<br />
<br />
== Programmers, Evaluation boards, and Software ==<br />
<br />
The devices are worth not very much, it is the support you get what matters. Instead of comparing devices, what needs to be compared are the software, development tools, community, and available support.<br />
<br />
<br />
* '''Atmel'''. Win-CUPL Design Software is provided for free. An ATF15XX-DK3 CPLD Development/Programmer Kit is available. ProChip Designer V5.0 is a pro design suite. ''Eval boards?''. Note: the software and the kit seem to be a bit dated (Windows XP is specified, etc).<br />
* '''Texas Instruments'''. No software, programmers, or evaluation kits are available from TI, but generic PAL programmers can be used.<br />
* '''Altera Corporation'''. Several development kits are available. Some, however, are from third-party sources. Devices seem to need a lot of other devices for support on the eval boards.<br />
* '''Lattice Semiconductor Corporation'''. Plenty of evaluation boards, breakout boards, etc are avalable. All eval boards and software are up to date.<br />
* '''Xilinx Inc'''. For $59, a CoolRunner-II CPLD Starter Kit is available with an evaluation board, programmer, software, and plenty of documentation.<br />
* '''Microsemi SoC (Actel)'''. For $99 you get the Starter Kit with an evaluation board, programmer, software, and documentation.</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Programmable_Logic_Devices&diff=1452
Programmable Logic Devices
2015-10-17T18:17:24Z
<p>Mkrdwiki: /* SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available */</p>
<hr />
<div>This page will cover simple PLD devices useable for hobby, prototyping, and similar applications. Costs are for quantity of 1 (one). Some devices (like Lattice Semiconductor MachXO3 FPGA's) are available as BGA package only. As available from Digi-Key. Last parsing 5Sept14. <br />
<br />
Most manufacturers are discontinuing production of PLDs, with the attention going to FPGAs, CPLDs, ASICs, and microprocessors / microcontrollers.<br />
<br />
<br />
The following are the remaining devices which are still being manufactured and are not under EOL (End of Life) / Discontinued notices. <br />
<br />
<br />
== PLDs (PAL, PLA, GAL, SPLD): ==<br />
<br />
* '''Atmel'''<br />
** '''ATF Family'''<br />
<br />
[http://www.atmel.com/products/Other/spld-cpld/spld-industry_standard.aspx]<br />
<br />
<br />
* '''Texas Instruments'''<br />
** '''PAL Family'''<br />
** '''TIBPAL Family'''<br />
** '''TICPAL Family'''<br />
<br />
[http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?familyId=317&family=logic&uiTemplateId=SZVI_T]<br />
<br />
<br />
== Cheap CPLDs - LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Atmel'''<br />
** '''ATF15xx'''. [http://www.atmel.com/products/Other/spld-cpld/cpld_atf15xx_family-industry_standard_compatible.aspx]<br />
** '''ATF750'''. [http://www.atmel.com/products/Other/spld-cpld/cpld-2_22v10s_in_24-pin_and_28-pin_packages.aspx]<br />
** '''ATF2500C'''. [http://www.atmel.com/devices/ATF2500C.aspx]<br />
<br />
<br />
* '''Altera Corporation'''<br />
** '''MAX 3000A Family'''<br />
** '''MAX 7000 Family'''<br />
** '''MAX Family'''<br />
** '''MAX II Family'''<br />
** '''MAX V Family'''<br />
[http://www.altera.com/devices/cpld/cpld-index.html]<br />
<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''ispMACH''' series<br />
** '''ispMACH 4000''' series<br />
** '''ispMACH 4A''' series<br />
** '''ispLSI 2000''' series<br />
** '''ispLSI 1000''' series<br />
[http://www.latticesemi.com/products/cpld/index.cfm]<br />
<br />
<br />
* '''Xilinx Inc'''<br />
** '''CoolRunner II'''<br />
** <strike>'''CoolRunner XPLA3'''</strike>. Mature (not for new designs) / discontinued.<br />
** '''XC9500XL'''<br />
[http://www.xilinx.com/products/silicon-devices/cpld/index.htm]<br />
<br />
== SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''iCE40 Family'''. LM, LP, HX. Tiny device, oriented for very low power, very small size, and mobile applications. Almost all package offerings are BGA. '''LM in BGA packages only (not for prototyping, hobbyist, student, low-volume).''' LP / HX two SMD packages (VQFP, TQFP) available.<br />
** '''iCE40 Family'''. Ultra / UltraLite. Tiny device, oriented for very low power, very small size, and mobile applications. The iCE40 UltraLite is available in BGA or FN (Flat, No Leads – generally not hand solderable) packages only. The iCE40 UltraLite is available in BGA packages only. Programmed with the iCEcube2 Design Software only (not Lattice Diamond). VCCIO 3.3V or less. '''Not for prototyping, hobbyist, student, low-volume.'''<br />
** '''MachXO Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip.<br />
** '''MachXO2 Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip. VCCIO 3.3V or less.<br />
** '''MachXO3 Family'''. Low power, instant-on, non-volatile FPGA. '''BGA packages only (not for prototyping, hobbyist, student, low-volume)'''. VCCIO 3.3V or less. <br />
** <strike>'''LatticeECP & EC Families'''</strike>. Mature (not for new designs).<br />
[http://www.latticesemi.com/products/fpga/index.cfm?source=topnav]<br />
<br />
Royalty-free LatticeMico8 8-bit microprocessor soft core available for MachXO2 devices.<br />
<br />
<br />
* '''Microsemi SoC (Actel)'''<br />
** '''ProASIC3 nano'''. Non-volatile.<br />
** '''ProASIC3'''. Non-volatile.<br />
** '''IGLOO'''. Non-volatile.<br />
** '''IGLOO nano'''. Non-volatile.<br />
[http://www.actel.com/products/devices.aspx]<br />
<br />
Royalty-free ARM Cortex-M1 32-bit microprocessor soft core available<br />
<br />
<br />
* '''Xilinx'''<br />
** <strike>'''Spartan'''</strike>. Mature (not for new designs) / discontinued. <br />
** <strike>'''Spartan-II'''</strike>. Mature (not for new designs) / discontinued. <br />
** '''Spartan-3A'''. Volatile. <br />
** '''Spartan-3AN'''. Non-volatile.<br />
<br />
Soft-cores 8-bit PicoBlaze Controller and 32-bit MicroBlaze Processor are available.<br />
<br />
== Programmers, Evaluation boards, and Software ==<br />
<br />
The devices are worth not very much, it is the support you get what matters. Instead of comparing devices, what needs to be compared are the software, development tools, community, and available support.<br />
<br />
<br />
* '''Atmel'''. Win-CUPL Design Software is provided for free. An ATF15XX-DK3 CPLD Development/Programmer Kit is available. ProChip Designer V5.0 is a pro design suite. ''Eval boards?''. Note: the software and the kit seem to be a bit dated (Windows XP is specified, etc).<br />
* '''Texas Instruments'''. No software, programmers, or evaluation kits are available from TI, but generic PAL programmers can be used.<br />
* '''Altera Corporation'''. Several development kits are available. Some, however, are from third-party sources. Devices seem to need a lot of other devices for support on the eval boards.<br />
* '''Lattice Semiconductor Corporation'''. Plenty of evaluation boards, breakout boards, etc are avalable. All eval boards and software are up to date.<br />
* '''Xilinx Inc'''. For $59, a CoolRunner-II CPLD Starter Kit is available with an evaluation board, programmer, software, and plenty of documentation.<br />
* '''Microsemi SoC (Actel)'''. For $99 you get the Starter Kit with an evaluation board, programmer, software, and documentation.</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Programmable_Logic_Devices&diff=1451
Programmable Logic Devices
2015-10-17T18:13:52Z
<p>Mkrdwiki: /* SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available */</p>
<hr />
<div>This page will cover simple PLD devices useable for hobby, prototyping, and similar applications. Costs are for quantity of 1 (one). Some devices (like Lattice Semiconductor MachXO3 FPGA's) are available as BGA package only. As available from Digi-Key. Last parsing 5Sept14. <br />
<br />
Most manufacturers are discontinuing production of PLDs, with the attention going to FPGAs, CPLDs, ASICs, and microprocessors / microcontrollers.<br />
<br />
<br />
The following are the remaining devices which are still being manufactured and are not under EOL (End of Life) / Discontinued notices. <br />
<br />
<br />
== PLDs (PAL, PLA, GAL, SPLD): ==<br />
<br />
* '''Atmel'''<br />
** '''ATF Family'''<br />
<br />
[http://www.atmel.com/products/Other/spld-cpld/spld-industry_standard.aspx]<br />
<br />
<br />
* '''Texas Instruments'''<br />
** '''PAL Family'''<br />
** '''TIBPAL Family'''<br />
** '''TICPAL Family'''<br />
<br />
[http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?familyId=317&family=logic&uiTemplateId=SZVI_T]<br />
<br />
<br />
== Cheap CPLDs - LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Atmel'''<br />
** '''ATF15xx'''. [http://www.atmel.com/products/Other/spld-cpld/cpld_atf15xx_family-industry_standard_compatible.aspx]<br />
** '''ATF750'''. [http://www.atmel.com/products/Other/spld-cpld/cpld-2_22v10s_in_24-pin_and_28-pin_packages.aspx]<br />
** '''ATF2500C'''. [http://www.atmel.com/devices/ATF2500C.aspx]<br />
<br />
<br />
* '''Altera Corporation'''<br />
** '''MAX 3000A Family'''<br />
** '''MAX 7000 Family'''<br />
** '''MAX Family'''<br />
** '''MAX II Family'''<br />
** '''MAX V Family'''<br />
[http://www.altera.com/devices/cpld/cpld-index.html]<br />
<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''ispMACH''' series<br />
** '''ispMACH 4000''' series<br />
** '''ispMACH 4A''' series<br />
** '''ispLSI 2000''' series<br />
** '''ispLSI 1000''' series<br />
[http://www.latticesemi.com/products/cpld/index.cfm]<br />
<br />
<br />
* '''Xilinx Inc'''<br />
** '''CoolRunner II'''<br />
** <strike>'''CoolRunner XPLA3'''</strike>. Mature (not for new designs) / discontinued.<br />
** '''XC9500XL'''<br />
[http://www.xilinx.com/products/silicon-devices/cpld/index.htm]<br />
<br />
== SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''iCE40 Family'''. LM, LP, HX. Tiny device, oriented for very low power, very small size, and mobile applications. Almost all package offerings are BGA. '''LM in BGA packages only (not for prototyping, hobbyist, student, low-volume).'''<br />
** '''iCE40 Family'''. Ultra / UltraLite. Tiny device, oriented for very low power, very small size, and mobile applications. The iCE40 UltraLite is available in BGA or FN (Flat, No Leads – generally not hand solderable) packages only. The iCE40 UltraLite is available in BGA packages only. Programmed with the iCEcube2 Design Software only (not Lattice Diamond). VCCIO 3.3V or less. '''Not for prototyping, hobbyist, student, low-volume.'''<br />
** '''MachXO Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip.<br />
** '''MachXO2 Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip. VCCIO 3.3V or less.<br />
** '''MachXO3 Family'''. Low power, instant-on, non-volatile FPGA. '''BGA packages only (not for prototyping, hobbyist, student, low-volume)'''. VCCIO 3.3V or less. <br />
** <strike>'''LatticeECP & EC Families'''</strike>. Mature (not for new designs).<br />
[http://www.latticesemi.com/products/fpga/index.cfm?source=topnav]<br />
<br />
Royalty-free LatticeMico8 8-bit microprocessor soft core available for MachXO2 devices.<br />
<br />
<br />
* '''Microsemi SoC (Actel)'''<br />
** '''ProASIC3 nano'''. Non-volatile.<br />
** '''ProASIC3'''. Non-volatile.<br />
** '''IGLOO'''. Non-volatile.<br />
** '''IGLOO nano'''. Non-volatile.<br />
[http://www.actel.com/products/devices.aspx]<br />
<br />
Royalty-free ARM Cortex-M1 32-bit microprocessor soft core available<br />
<br />
<br />
* '''Xilinx'''<br />
** <strike>'''Spartan'''</strike>. Mature (not for new designs) / discontinued. <br />
** <strike>'''Spartan-II'''</strike>. Mature (not for new designs) / discontinued. <br />
** '''Spartan-3A'''. Volatile. <br />
** '''Spartan-3AN'''. Non-volatile.<br />
<br />
Soft-cores 8-bit PicoBlaze Controller and 32-bit MicroBlaze Processor are available.<br />
<br />
== Programmers, Evaluation boards, and Software ==<br />
<br />
The devices are worth not very much, it is the support you get what matters. Instead of comparing devices, what needs to be compared are the software, development tools, community, and available support.<br />
<br />
<br />
* '''Atmel'''. Win-CUPL Design Software is provided for free. An ATF15XX-DK3 CPLD Development/Programmer Kit is available. ProChip Designer V5.0 is a pro design suite. ''Eval boards?''. Note: the software and the kit seem to be a bit dated (Windows XP is specified, etc).<br />
* '''Texas Instruments'''. No software, programmers, or evaluation kits are available from TI, but generic PAL programmers can be used.<br />
* '''Altera Corporation'''. Several development kits are available. Some, however, are from third-party sources. Devices seem to need a lot of other devices for support on the eval boards.<br />
* '''Lattice Semiconductor Corporation'''. Plenty of evaluation boards, breakout boards, etc are avalable. All eval boards and software are up to date.<br />
* '''Xilinx Inc'''. For $59, a CoolRunner-II CPLD Starter Kit is available with an evaluation board, programmer, software, and plenty of documentation.<br />
* '''Microsemi SoC (Actel)'''. For $99 you get the Starter Kit with an evaluation board, programmer, software, and documentation.</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Programmable_Logic_Devices&diff=1450
Programmable Logic Devices
2015-10-17T18:04:06Z
<p>Mkrdwiki: /* SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available */</p>
<hr />
<div>This page will cover simple PLD devices useable for hobby, prototyping, and similar applications. Costs are for quantity of 1 (one). Some devices (like Lattice Semiconductor MachXO3 FPGA's) are available as BGA package only. As available from Digi-Key. Last parsing 5Sept14. <br />
<br />
Most manufacturers are discontinuing production of PLDs, with the attention going to FPGAs, CPLDs, ASICs, and microprocessors / microcontrollers.<br />
<br />
<br />
The following are the remaining devices which are still being manufactured and are not under EOL (End of Life) / Discontinued notices. <br />
<br />
<br />
== PLDs (PAL, PLA, GAL, SPLD): ==<br />
<br />
* '''Atmel'''<br />
** '''ATF Family'''<br />
<br />
[http://www.atmel.com/products/Other/spld-cpld/spld-industry_standard.aspx]<br />
<br />
<br />
* '''Texas Instruments'''<br />
** '''PAL Family'''<br />
** '''TIBPAL Family'''<br />
** '''TICPAL Family'''<br />
<br />
[http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?familyId=317&family=logic&uiTemplateId=SZVI_T]<br />
<br />
<br />
== Cheap CPLDs - LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Atmel'''<br />
** '''ATF15xx'''. [http://www.atmel.com/products/Other/spld-cpld/cpld_atf15xx_family-industry_standard_compatible.aspx]<br />
** '''ATF750'''. [http://www.atmel.com/products/Other/spld-cpld/cpld-2_22v10s_in_24-pin_and_28-pin_packages.aspx]<br />
** '''ATF2500C'''. [http://www.atmel.com/devices/ATF2500C.aspx]<br />
<br />
<br />
* '''Altera Corporation'''<br />
** '''MAX 3000A Family'''<br />
** '''MAX 7000 Family'''<br />
** '''MAX Family'''<br />
** '''MAX II Family'''<br />
** '''MAX V Family'''<br />
[http://www.altera.com/devices/cpld/cpld-index.html]<br />
<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''ispMACH''' series<br />
** '''ispMACH 4000''' series<br />
** '''ispMACH 4A''' series<br />
** '''ispLSI 2000''' series<br />
** '''ispLSI 1000''' series<br />
[http://www.latticesemi.com/products/cpld/index.cfm]<br />
<br />
<br />
* '''Xilinx Inc'''<br />
** '''CoolRunner II'''<br />
** <strike>'''CoolRunner XPLA3'''</strike>. Mature (not for new designs) / discontinued.<br />
** '''XC9500XL'''<br />
[http://www.xilinx.com/products/silicon-devices/cpld/index.htm]<br />
<br />
== SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''iCE40 Family'''. LM, LP, HX. Tiny device, oriented for very low power, very small size, and mobile applications. Almost all package offerings are BGA. '''LM in BGA packages only (not for prototyping, hobbyist, student, low-volume)'''<br />
** '''MachXO Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip.<br />
** '''MachXO2 Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip. VCCIO 3.3V or less.<br />
** '''MachXO3 Family'''. Low power, instant-on, non-volatile FPGA. '''BGA packages only (not for prototyping, hobbyist, student, low-volume)'''. VCCIO 3.3V or less. <br />
** <strike>'''LatticeECP & EC Families'''</strike>. Mature (not for new designs).<br />
[http://www.latticesemi.com/products/fpga/index.cfm?source=topnav]<br />
<br />
Royalty-free LatticeMico8 8-bit microprocessor soft core available for MachXO2 devices.<br />
<br />
<br />
* '''Microsemi SoC (Actel)'''<br />
** '''ProASIC3 nano'''. Non-volatile.<br />
** '''ProASIC3'''. Non-volatile.<br />
** '''IGLOO'''. Non-volatile.<br />
** '''IGLOO nano'''. Non-volatile.<br />
[http://www.actel.com/products/devices.aspx]<br />
<br />
Royalty-free ARM Cortex-M1 32-bit microprocessor soft core available<br />
<br />
<br />
* '''Xilinx'''<br />
** <strike>'''Spartan'''</strike>. Mature (not for new designs) / discontinued. <br />
** <strike>'''Spartan-II'''</strike>. Mature (not for new designs) / discontinued. <br />
** '''Spartan-3A'''. Volatile. <br />
** '''Spartan-3AN'''. Non-volatile.<br />
<br />
Soft-cores 8-bit PicoBlaze Controller and 32-bit MicroBlaze Processor are available.<br />
<br />
== Programmers, Evaluation boards, and Software ==<br />
<br />
The devices are worth not very much, it is the support you get what matters. Instead of comparing devices, what needs to be compared are the software, development tools, community, and available support.<br />
<br />
<br />
* '''Atmel'''. Win-CUPL Design Software is provided for free. An ATF15XX-DK3 CPLD Development/Programmer Kit is available. ProChip Designer V5.0 is a pro design suite. ''Eval boards?''. Note: the software and the kit seem to be a bit dated (Windows XP is specified, etc).<br />
* '''Texas Instruments'''. No software, programmers, or evaluation kits are available from TI, but generic PAL programmers can be used.<br />
* '''Altera Corporation'''. Several development kits are available. Some, however, are from third-party sources. Devices seem to need a lot of other devices for support on the eval boards.<br />
* '''Lattice Semiconductor Corporation'''. Plenty of evaluation boards, breakout boards, etc are avalable. All eval boards and software are up to date.<br />
* '''Xilinx Inc'''. For $59, a CoolRunner-II CPLD Starter Kit is available with an evaluation board, programmer, software, and plenty of documentation.<br />
* '''Microsemi SoC (Actel)'''. For $99 you get the Starter Kit with an evaluation board, programmer, software, and documentation.</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Programmable_Logic_Devices&diff=1449
Programmable Logic Devices
2015-10-17T17:58:45Z
<p>Mkrdwiki: /* SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available */</p>
<hr />
<div>This page will cover simple PLD devices useable for hobby, prototyping, and similar applications. Costs are for quantity of 1 (one). Some devices (like Lattice Semiconductor MachXO3 FPGA's) are available as BGA package only. As available from Digi-Key. Last parsing 5Sept14. <br />
<br />
Most manufacturers are discontinuing production of PLDs, with the attention going to FPGAs, CPLDs, ASICs, and microprocessors / microcontrollers.<br />
<br />
<br />
The following are the remaining devices which are still being manufactured and are not under EOL (End of Life) / Discontinued notices. <br />
<br />
<br />
== PLDs (PAL, PLA, GAL, SPLD): ==<br />
<br />
* '''Atmel'''<br />
** '''ATF Family'''<br />
<br />
[http://www.atmel.com/products/Other/spld-cpld/spld-industry_standard.aspx]<br />
<br />
<br />
* '''Texas Instruments'''<br />
** '''PAL Family'''<br />
** '''TIBPAL Family'''<br />
** '''TICPAL Family'''<br />
<br />
[http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?familyId=317&family=logic&uiTemplateId=SZVI_T]<br />
<br />
<br />
== Cheap CPLDs - LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Atmel'''<br />
** '''ATF15xx'''. [http://www.atmel.com/products/Other/spld-cpld/cpld_atf15xx_family-industry_standard_compatible.aspx]<br />
** '''ATF750'''. [http://www.atmel.com/products/Other/spld-cpld/cpld-2_22v10s_in_24-pin_and_28-pin_packages.aspx]<br />
** '''ATF2500C'''. [http://www.atmel.com/devices/ATF2500C.aspx]<br />
<br />
<br />
* '''Altera Corporation'''<br />
** '''MAX 3000A Family'''<br />
** '''MAX 7000 Family'''<br />
** '''MAX Family'''<br />
** '''MAX II Family'''<br />
** '''MAX V Family'''<br />
[http://www.altera.com/devices/cpld/cpld-index.html]<br />
<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''ispMACH''' series<br />
** '''ispMACH 4000''' series<br />
** '''ispMACH 4A''' series<br />
** '''ispLSI 2000''' series<br />
** '''ispLSI 1000''' series<br />
[http://www.latticesemi.com/products/cpld/index.cfm]<br />
<br />
<br />
* '''Xilinx Inc'''<br />
** '''CoolRunner II'''<br />
** <strike>'''CoolRunner XPLA3'''</strike>. Mature (not for new designs) / discontinued.<br />
** '''XC9500XL'''<br />
[http://www.xilinx.com/products/silicon-devices/cpld/index.htm]<br />
<br />
== SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''iCE40 Family'''. Tiny device, oriented for very low power, very small size, and mobile applications. Almost all package offerings are BGA.<br />
** '''MachXO Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip.<br />
** '''MachXO2 Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip. VCCIO 3.3V or less.<br />
** '''MachXO3 Family'''. Low power, instant-on, non-volatile FPGA. '''BGA packages only (not for prototyping, hobbyist, student, low-volume)'''. VCCIO 3.3V or less. <br />
** <strike>'''LatticeECP & EC Families'''</strike>. Mature (not for new designs).<br />
[http://www.latticesemi.com/products/fpga/index.cfm?source=topnav]<br />
<br />
Royalty-free LatticeMico8 8-bit microprocessor soft core available for MachXO2 devices.<br />
<br />
<br />
* '''Microsemi SoC (Actel)'''<br />
** '''ProASIC3 nano'''. Non-volatile.<br />
** '''ProASIC3'''. Non-volatile.<br />
** '''IGLOO'''. Non-volatile.<br />
** '''IGLOO nano'''. Non-volatile.<br />
[http://www.actel.com/products/devices.aspx]<br />
<br />
Royalty-free ARM Cortex-M1 32-bit microprocessor soft core available<br />
<br />
<br />
* '''Xilinx'''<br />
** <strike>'''Spartan'''</strike>. Mature (not for new designs) / discontinued. <br />
** <strike>'''Spartan-II'''</strike>. Mature (not for new designs) / discontinued. <br />
** '''Spartan-3A'''. Volatile. <br />
** '''Spartan-3AN'''. Non-volatile.<br />
<br />
Soft-cores 8-bit PicoBlaze Controller and 32-bit MicroBlaze Processor are available.<br />
<br />
== Programmers, Evaluation boards, and Software ==<br />
<br />
The devices are worth not very much, it is the support you get what matters. Instead of comparing devices, what needs to be compared are the software, development tools, community, and available support.<br />
<br />
<br />
* '''Atmel'''. Win-CUPL Design Software is provided for free. An ATF15XX-DK3 CPLD Development/Programmer Kit is available. ProChip Designer V5.0 is a pro design suite. ''Eval boards?''. Note: the software and the kit seem to be a bit dated (Windows XP is specified, etc).<br />
* '''Texas Instruments'''. No software, programmers, or evaluation kits are available from TI, but generic PAL programmers can be used.<br />
* '''Altera Corporation'''. Several development kits are available. Some, however, are from third-party sources. Devices seem to need a lot of other devices for support on the eval boards.<br />
* '''Lattice Semiconductor Corporation'''. Plenty of evaluation boards, breakout boards, etc are avalable. All eval boards and software are up to date.<br />
* '''Xilinx Inc'''. For $59, a CoolRunner-II CPLD Starter Kit is available with an evaluation board, programmer, software, and plenty of documentation.<br />
* '''Microsemi SoC (Actel)'''. For $99 you get the Starter Kit with an evaluation board, programmer, software, and documentation.</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Programmable_Logic_Devices&diff=1448
Programmable Logic Devices
2015-10-17T17:39:24Z
<p>Mkrdwiki: /* SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available */</p>
<hr />
<div>This page will cover simple PLD devices useable for hobby, prototyping, and similar applications. Costs are for quantity of 1 (one). Some devices (like Lattice Semiconductor MachXO3 FPGA's) are available as BGA package only. As available from Digi-Key. Last parsing 5Sept14. <br />
<br />
Most manufacturers are discontinuing production of PLDs, with the attention going to FPGAs, CPLDs, ASICs, and microprocessors / microcontrollers.<br />
<br />
<br />
The following are the remaining devices which are still being manufactured and are not under EOL (End of Life) / Discontinued notices. <br />
<br />
<br />
== PLDs (PAL, PLA, GAL, SPLD): ==<br />
<br />
* '''Atmel'''<br />
** '''ATF Family'''<br />
<br />
[http://www.atmel.com/products/Other/spld-cpld/spld-industry_standard.aspx]<br />
<br />
<br />
* '''Texas Instruments'''<br />
** '''PAL Family'''<br />
** '''TIBPAL Family'''<br />
** '''TICPAL Family'''<br />
<br />
[http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?familyId=317&family=logic&uiTemplateId=SZVI_T]<br />
<br />
<br />
== Cheap CPLDs - LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Atmel'''<br />
** '''ATF15xx'''. [http://www.atmel.com/products/Other/spld-cpld/cpld_atf15xx_family-industry_standard_compatible.aspx]<br />
** '''ATF750'''. [http://www.atmel.com/products/Other/spld-cpld/cpld-2_22v10s_in_24-pin_and_28-pin_packages.aspx]<br />
** '''ATF2500C'''. [http://www.atmel.com/devices/ATF2500C.aspx]<br />
<br />
<br />
* '''Altera Corporation'''<br />
** '''MAX 3000A Family'''<br />
** '''MAX 7000 Family'''<br />
** '''MAX Family'''<br />
** '''MAX II Family'''<br />
** '''MAX V Family'''<br />
[http://www.altera.com/devices/cpld/cpld-index.html]<br />
<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''ispMACH''' series<br />
** '''ispMACH 4000''' series<br />
** '''ispMACH 4A''' series<br />
** '''ispLSI 2000''' series<br />
** '''ispLSI 1000''' series<br />
[http://www.latticesemi.com/products/cpld/index.cfm]<br />
<br />
<br />
* '''Xilinx Inc'''<br />
** '''CoolRunner II'''<br />
** <strike>'''CoolRunner XPLA3'''</strike>. Mature (not for new designs) / discontinued.<br />
** '''XC9500XL'''<br />
[http://www.xilinx.com/products/silicon-devices/cpld/index.htm]<br />
<br />
== SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''iCE40 Family'''. Tiny device, oriented for very low power, very small size, and mobile applications. Almost all package offerings are BGA.<br />
** '''MachXO Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip.<br />
** '''MachXO2 Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip. VCCIO 3.3V or less.<br />
** '''MachXO3 Family'''. Low power, instant-on, non-volatile FPGA. BGA packages only. VCCIO 3.3V or less. <br />
** <strike>'''LatticeECP & EC Families'''</strike>. Mature (not for new designs).<br />
[http://www.latticesemi.com/products/fpga/index.cfm?source=topnav]<br />
<br />
Royalty-free LatticeMico8 8-bit microprocessor soft core available for MachXO2 devices.<br />
<br />
<br />
* '''Microsemi SoC (Actel)'''<br />
** '''ProASIC3 nano'''. Non-volatile.<br />
** '''ProASIC3'''. Non-volatile.<br />
** '''IGLOO'''. Non-volatile.<br />
** '''IGLOO nano'''. Non-volatile.<br />
[http://www.actel.com/products/devices.aspx]<br />
<br />
Royalty-free ARM Cortex-M1 32-bit microprocessor soft core available<br />
<br />
<br />
* '''Xilinx'''<br />
** <strike>'''Spartan'''</strike>. Mature (not for new designs) / discontinued. <br />
** <strike>'''Spartan-II'''</strike>. Mature (not for new designs) / discontinued. <br />
** '''Spartan-3A'''. Volatile. <br />
** '''Spartan-3AN'''. Non-volatile.<br />
<br />
Soft-cores 8-bit PicoBlaze Controller and 32-bit MicroBlaze Processor are available.<br />
<br />
== Programmers, Evaluation boards, and Software ==<br />
<br />
The devices are worth not very much, it is the support you get what matters. Instead of comparing devices, what needs to be compared are the software, development tools, community, and available support.<br />
<br />
<br />
* '''Atmel'''. Win-CUPL Design Software is provided for free. An ATF15XX-DK3 CPLD Development/Programmer Kit is available. ProChip Designer V5.0 is a pro design suite. ''Eval boards?''. Note: the software and the kit seem to be a bit dated (Windows XP is specified, etc).<br />
* '''Texas Instruments'''. No software, programmers, or evaluation kits are available from TI, but generic PAL programmers can be used.<br />
* '''Altera Corporation'''. Several development kits are available. Some, however, are from third-party sources. Devices seem to need a lot of other devices for support on the eval boards.<br />
* '''Lattice Semiconductor Corporation'''. Plenty of evaluation boards, breakout boards, etc are avalable. All eval boards and software are up to date.<br />
* '''Xilinx Inc'''. For $59, a CoolRunner-II CPLD Starter Kit is available with an evaluation board, programmer, software, and plenty of documentation.<br />
* '''Microsemi SoC (Actel)'''. For $99 you get the Starter Kit with an evaluation board, programmer, software, and documentation.</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Programmable_Logic_Devices&diff=1447
Programmable Logic Devices
2015-10-17T17:27:22Z
<p>Mkrdwiki: /* SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available */</p>
<hr />
<div>This page will cover simple PLD devices useable for hobby, prototyping, and similar applications. Costs are for quantity of 1 (one). Some devices (like Lattice Semiconductor MachXO3 FPGA's) are available as BGA package only. As available from Digi-Key. Last parsing 5Sept14. <br />
<br />
Most manufacturers are discontinuing production of PLDs, with the attention going to FPGAs, CPLDs, ASICs, and microprocessors / microcontrollers.<br />
<br />
<br />
The following are the remaining devices which are still being manufactured and are not under EOL (End of Life) / Discontinued notices. <br />
<br />
<br />
== PLDs (PAL, PLA, GAL, SPLD): ==<br />
<br />
* '''Atmel'''<br />
** '''ATF Family'''<br />
<br />
[http://www.atmel.com/products/Other/spld-cpld/spld-industry_standard.aspx]<br />
<br />
<br />
* '''Texas Instruments'''<br />
** '''PAL Family'''<br />
** '''TIBPAL Family'''<br />
** '''TICPAL Family'''<br />
<br />
[http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?familyId=317&family=logic&uiTemplateId=SZVI_T]<br />
<br />
<br />
== Cheap CPLDs - LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Atmel'''<br />
** '''ATF15xx'''. [http://www.atmel.com/products/Other/spld-cpld/cpld_atf15xx_family-industry_standard_compatible.aspx]<br />
** '''ATF750'''. [http://www.atmel.com/products/Other/spld-cpld/cpld-2_22v10s_in_24-pin_and_28-pin_packages.aspx]<br />
** '''ATF2500C'''. [http://www.atmel.com/devices/ATF2500C.aspx]<br />
<br />
<br />
* '''Altera Corporation'''<br />
** '''MAX 3000A Family'''<br />
** '''MAX 7000 Family'''<br />
** '''MAX Family'''<br />
** '''MAX II Family'''<br />
** '''MAX V Family'''<br />
[http://www.altera.com/devices/cpld/cpld-index.html]<br />
<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''ispMACH''' series<br />
** '''ispMACH 4000''' series<br />
** '''ispMACH 4A''' series<br />
** '''ispLSI 2000''' series<br />
** '''ispLSI 1000''' series<br />
[http://www.latticesemi.com/products/cpld/index.cfm]<br />
<br />
<br />
* '''Xilinx Inc'''<br />
** '''CoolRunner II'''<br />
** <strike>'''CoolRunner XPLA3'''</strike>. Mature (not for new designs) / discontinued.<br />
** '''XC9500XL'''<br />
[http://www.xilinx.com/products/silicon-devices/cpld/index.htm]<br />
<br />
== SMALL FPGAs – LESS THAN $10 or less than 40 IO devices available ==<br />
<br />
* '''Lattice Semiconductor Corporation'''<br />
** '''iCE40 Family'''. Tiny device, oriented for very low power, very small size, and mobile applications. Almost all package offerings are BGA.<br />
** '''MachXO Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip.<br />
** '''MachXO2 Family'''. Tiny device with FLASH internal configuration memory. Non-volatile, near instant-on, no need for external memory chip.<br />
** '''MachXO3 Family'''. Low power, instant-on, non-volatile FPGA. BGA packages only. 324-ball csfBGA1 (10 mm x 10 mm, 0.5 mm) and smaller packages are only available for E=1.2 V devices. Not suitable for hobbyist. <br />
** <strike>'''LatticeECP & EC Families'''</strike>. Mature (not for new designs).<br />
[http://www.latticesemi.com/products/fpga/index.cfm?source=topnav]<br />
<br />
Royalty-free LatticeMico8 8-bit microprocessor soft core available for MachXO2 devices.<br />
<br />
<br />
* '''Microsemi SoC (Actel)'''<br />
** '''ProASIC3 nano'''. Non-volatile.<br />
** '''ProASIC3'''. Non-volatile.<br />
** '''IGLOO'''. Non-volatile.<br />
** '''IGLOO nano'''. Non-volatile.<br />
[http://www.actel.com/products/devices.aspx]<br />
<br />
Royalty-free ARM Cortex-M1 32-bit microprocessor soft core available<br />
<br />
<br />
* '''Xilinx'''<br />
** <strike>'''Spartan'''</strike>. Mature (not for new designs) / discontinued. <br />
** <strike>'''Spartan-II'''</strike>. Mature (not for new designs) / discontinued. <br />
** '''Spartan-3A'''. Volatile. <br />
** '''Spartan-3AN'''. Non-volatile.<br />
<br />
Soft-cores 8-bit PicoBlaze Controller and 32-bit MicroBlaze Processor are available.<br />
<br />
== Programmers, Evaluation boards, and Software ==<br />
<br />
The devices are worth not very much, it is the support you get what matters. Instead of comparing devices, what needs to be compared are the software, development tools, community, and available support.<br />
<br />
<br />
* '''Atmel'''. Win-CUPL Design Software is provided for free. An ATF15XX-DK3 CPLD Development/Programmer Kit is available. ProChip Designer V5.0 is a pro design suite. ''Eval boards?''. Note: the software and the kit seem to be a bit dated (Windows XP is specified, etc).<br />
* '''Texas Instruments'''. No software, programmers, or evaluation kits are available from TI, but generic PAL programmers can be used.<br />
* '''Altera Corporation'''. Several development kits are available. Some, however, are from third-party sources. Devices seem to need a lot of other devices for support on the eval boards.<br />
* '''Lattice Semiconductor Corporation'''. Plenty of evaluation boards, breakout boards, etc are avalable. All eval boards and software are up to date.<br />
* '''Xilinx Inc'''. For $59, a CoolRunner-II CPLD Starter Kit is available with an evaluation board, programmer, software, and plenty of documentation.<br />
* '''Microsemi SoC (Actel)'''. For $99 you get the Starter Kit with an evaluation board, programmer, software, and documentation.</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1446
Buck Voltage Regulator Evaluation Project
2015-07-07T03:15:15Z
<p>Mkrdwiki: /* Schematic */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[File:Figure 5.2 Webench Schematic.png|thumb|Figure 5.2: Webench Schematic]]<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM TODO ADD</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
<br />
<br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging.<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor TODO ADD<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
TODO ADD<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
TODO ADD Thermal image of 30-min operation after change.<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report.<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge.<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=File:Figure_5.2_Webench_Schematic.png&diff=1445
File:Figure 5.2 Webench Schematic.png
2015-07-07T03:14:51Z
<p>Mkrdwiki: Buck Voltage Regulator Evaluation Project: Webench Schematic</p>
<hr />
<div>Buck Voltage Regulator Evaluation Project: Webench Schematic</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1444
Buck Voltage Regulator Evaluation Project
2015-07-07T03:12:37Z
<p>Mkrdwiki: /* Schematic */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[File:Figure 5.2: Webench Schematic|thumb|Figure 5.2: Webench Schematic]]<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM TODO ADD</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
<br />
<br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging.<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor TODO ADD<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
TODO ADD<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
TODO ADD Thermal image of 30-min operation after change.<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report.<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge.<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1443
Buck Voltage Regulator Evaluation Project
2015-07-07T02:47:23Z
<p>Mkrdwiki: /* MOSFET, Active Switch */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
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<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM TODO ADD</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
<br />
<br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging.<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor TODO ADD<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
TODO ADD<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
TODO ADD Thermal image of 30-min operation after change.<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report.<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge.<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1442
Buck Voltage Regulator Evaluation Project
2015-07-07T02:47:09Z
<p>Mkrdwiki: /* MOSET, Synchronous Rectification */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM TODO ADD</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
<br />
<br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging.<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor TODO ADD<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
TODO ADD<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
TODO ADD Thermal image of 30-min operation after change.<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report.<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1441
Buck Voltage Regulator Evaluation Project
2015-07-07T02:43:16Z
<p>Mkrdwiki: /* Output Capacitance */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM TODO ADD</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
<br />
<br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging.<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor TODO ADD<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
TODO ADD<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
TODO ADD Thermal image of 30-min operation after change.<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report.<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1440
Buck Voltage Regulator Evaluation Project
2015-07-07T02:42:37Z
<p>Mkrdwiki: /* Snubber */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM TODO ADD</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
<br />
<br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging.<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor TODO ADD<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
TODO ADD<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
TODO ADD Thermal image of 30-min operation after change.<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report.<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1439
Buck Voltage Regulator Evaluation Project
2015-07-07T02:42:04Z
<p>Mkrdwiki: /* Power Supply */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM TODO ADD</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
<br />
<br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging.<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor TODO ADD<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
TODO ADD<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
TODO ADD Thermal image of 30-min operation after change.<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1438
Buck Voltage Regulator Evaluation Project
2015-07-07T02:41:14Z
<p>Mkrdwiki: /* Design Improvements */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM TODO ADD</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
<br />
<br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging.<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor TODO ADD<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
TODO ADD<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1437
Buck Voltage Regulator Evaluation Project
2015-07-07T02:39:29Z
<p>Mkrdwiki: /* Sense Resistor Current Waveform */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM TODO ADD</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
<br />
<br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging.<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor TODO ADD<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1436
Buck Voltage Regulator Evaluation Project
2015-07-07T02:38:44Z
<p>Mkrdwiki: /* Thermal Infra-Red Imaging Of Full-Load Operation */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM TODO ADD</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
<br />
<br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging.<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1435
Buck Voltage Regulator Evaluation Project
2015-07-07T02:36:26Z
<p>Mkrdwiki: /* Test Equipment Calibration Information */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM TODO ADD</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
<br />
<br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1434
Buck Voltage Regulator Evaluation Project
2015-07-07T02:35:51Z
<p>Mkrdwiki: /* Test Equipment Calibration Information */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
<br />
<br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
<br />
<br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1433
Buck Voltage Regulator Evaluation Project
2015-07-07T02:32:49Z
<p>Mkrdwiki: /* Circuit Simulation */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
TODO ADD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1432
Buck Voltage Regulator Evaluation Project
2015-07-07T02:32:25Z
<p>Mkrdwiki: /* MOSFET Active Rectifier */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
TODO ADD Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1431
Buck Voltage Regulator Evaluation Project
2015-07-07T02:32:03Z
<p>Mkrdwiki: /* MOSFET Active Rectifier */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
<br />
TODO ADD<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss.<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1430
Buck Voltage Regulator Evaluation Project
2015-07-07T02:31:46Z
<p>Mkrdwiki: /* MOSFET Switch */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1429
Buck Voltage Regulator Evaluation Project
2015-07-07T02:31:34Z
<p>Mkrdwiki: /* Input Filtering Capacitors */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
<br />
TODO ADD<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1428
Buck Voltage Regulator Evaluation Project
2015-07-07T02:30:26Z
<p>Mkrdwiki: /* Output Voltage Ripple */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (TODO ADD). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered.<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1427
Buck Voltage Regulator Evaluation Project
2015-07-07T02:29:08Z
<p>Mkrdwiki: /* Tolerance Stacking */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
<br />
TODO ADD<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1426
Buck Voltage Regulator Evaluation Project
2015-07-07T02:28:37Z
<p>Mkrdwiki: /* Online Design Tool */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench-suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1425
Buck Voltage Regulator Evaluation Project
2015-07-07T02:26:53Z
<p>Mkrdwiki: /* Project Design Requirements */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in [[Buck Voltage Regulator Evaluation Project#Tolerance Stacking]].<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1424
Buck Voltage Regulator Evaluation Project
2015-07-07T02:25:54Z
<p>Mkrdwiki: /* Online Design Tool */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project#Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1423
Buck Voltage Regulator Evaluation Project
2015-07-07T02:24:59Z
<p>Mkrdwiki: /* Online Design Tool */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see [[Buck Voltage Regulator Evaluation Project:Integrated Circuit (IC) Controller]]) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested.<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1422
Buck Voltage Regulator Evaluation Project
2015-07-07T02:23:03Z
<p>Mkrdwiki: /* System Level Diagram */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb|Figure 5.1: System Level Diagram]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=File:Figure_5.1-_System_Level_Diagram.png&diff=1421
File:Figure 5.1- System Level Diagram.png
2015-07-07T02:21:43Z
<p>Mkrdwiki: Buck Voltage Regulator Evaluation Project: System Level Diagram</p>
<hr />
<div>Buck Voltage Regulator Evaluation Project: System Level Diagram</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1420
Buck Voltage Regulator Evaluation Project
2015-07-07T02:19:21Z
<p>Mkrdwiki: /* System Level Diagram */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:Figure_5.1-_System_Level_Diagram.png|thumb]]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1419
Buck Voltage Regulator Evaluation Project
2015-07-07T02:18:27Z
<p>Mkrdwiki: /* System Level Diagram */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[File:'''Figure_5.1-_System_Level_Diagram.png|thumb''']]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1418
Buck Voltage Regulator Evaluation Project
2015-07-07T02:15:37Z
<p>Mkrdwiki: /* System Level Diagram */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[Image:|thumb|'''Figure_5.1-_System_Level_Diagram''']]<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1417
Buck Voltage Regulator Evaluation Project
2015-07-07T02:13:21Z
<p>Mkrdwiki: /* System Level Design */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[Image:|thumb|'''Figure 5.1: System Level Diagram''']]<br />
<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
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MKRD.info Wiki:Copyrights
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<div>ALL INFORMATION ON THIS WIKI IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2006-2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
<br />
<br />
Administrator of this Wiki, also Administrator of Main Website:<br />
<br />
http://www.MKRD.info/<br />
<br />
On-line Contact Form:<br />
<br />
http://mkrd.info/contact1.html</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=MKRD.info_Wiki:Copyrights&diff=1415
MKRD.info Wiki:Copyrights
2015-07-07T01:57:07Z
<p>Mkrdwiki: Created page with "ALL INFORMATION ON THIS WIKI IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION. ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMME..."</p>
<hr />
<div>ALL INFORMATION ON THIS WIKI IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
<br />
<br />
Administrator of this Wiki, also Administrator of Main Website:<br />
<br />
http://www.MKRD.info/<br />
<br />
On-line Contact Form:<br />
<br />
http://mkrd.info/contact1.html</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Electronics_as_a_Hobby_portal&diff=1414
Electronics as a Hobby portal
2015-07-07T01:55:47Z
<p>Mkrdwiki: </p>
<hr />
<div>* [[Intuitive Semiconductors textbook]]<br />
* [[Longest Distance Radio]]<br />
* [[Microcontrollers Roadmap]]<br />
* [[Soldering Flux Explained portal]]<br />
* [[Low Cost Basic Stamps]]<br />
* [[Electronics Suppliers and Distributors]]<br />
* [[Best Low-Power MOSFETs]]<br />
* [[Best High-Power MOSFETs]]<br />
* [[Complementary transistors]]<br />
* [[Electronic Device Identification portal]]<br />
* [[Programmable Logic portal]]<br />
* [[RadioShack Transistors Datasheets]]<br />
* [[Soldering HowTo]]<br />
* [[Basic Stamps]]<br />
* [[Electronics Books reviews]]<br />
* [[Articles on my main website related to electronics]]<br />
* [[How to troubleshoot a logic device]]<br />
* [[What is the proper amount of heatsink paste]]<br />
* [[Needle and SMD multimeter DMM probes]]<br />
* [[Troubleshooting complex boards]]<br />
* [[Schematic Capture]]<br />
* [[Switch bounce illustrated]]<br />
* [[Which parts distributor to use]]<br />
* [[Programmable Logic Devices]]<br />
* [[List of electronic parts distributors]]<br />
* [[DipTrace Review]]<br />
* [[How to measure capacitance in-circuit]]<br />
* [[BOOK PREVIEW: Transistors and Semiconductors: Clearly, Simply, Intuitively, and Concisely explained]]<br />
* [[Entry Level Amateur (Ham) Radio Article - Best Bands, Frequencies, Equipment]]<br />
* [[Reverse battery or DC polarity protection]]<br />
* [[How many connections are required for JTAG]]<br />
* [[What to look for in electronics troubleshooting]]<br />
* [[Promising to repair consumer electronics for family and friends]]<br />
* [[What is a zero ohm resistor and why is it called a resistor]]<br />
* [[Issues that every electrical engineer must be aware of]]<br />
* [[Buck Voltage Regulator Evaluation Project]]<br />
<br />
<br />
<br />
Life Goal – Make it so that “Electronics as a Hobby” is recognized as a valid term, gets wellknown, and becomes the most popular hobby. How the hell can it not be in the modern tech world where everything is run by electronics? Another as useful hobby or type of guy – hands-on mechanic or “golden hands” kind of guy. Life Goal – provide services for both<br />
<br />
<br />
electronics as a hobby, robotics, amateur and ham radio<br />
<br />
<br />
electronics textbooks<br />
<br />
<br />
<br />
For electronics:<br />
<br />
* make a website for hobby (small quantity solder, flux, novelty items, tools, and pcb manufacturing) products to solve all problems that I encountered.<br />
<br />
* missing content: make a page on analog multimeters<br />
<br />
* free ebook on required information for electronics hobbyists and technicians (stuff like where to buy stuff, soldering, measuring equipment, software, reference info, cross database for devices/semiconductors, how to read labels lk IC, super clear transistor book, RF design, no math theory, etc)<br />
<br />
* my task consolidate absolutely all knowledge on amateur electronics into a single reference<br />
* doc diff bw flip flop and latch<br />
<br />
* doc since i have never heard it mentioned: looks like none of profs and book authors ever had destroyed a resistor pot by rotating it to a low value and exceeding power limit. also, they have never burned finders from a hot component, solder heated component, or soldering iron.<br />
<br />
* wtf my circuits do not work, components fail, etc. how do engineers and companies do it. also extremely difficult to select among clones a single part<br />
<br />
* document phototransistor photointerrupter stupidities (no markings for easy reverse damage, no application note, wtf transistor load resistor is extremely low, amplifier and comparator required)<br />
<br />
* e electronics broken down into generic building blocks (fe parallel resistor block, emitter resistor, voltage divider, voltage drop, etc)<br />
<br />
* single buck/boost regulator, database of ones suitable for hobby prototype rework etc devices, as well as single devices easy enough for hobbyists to implement.<br />
<br />
* length of probes: Pomona small is too short, Pomona bigger one is OK or a bit too long<br />
<br />
* solve stupidity of wire ampacity lack of information<br />
<br />
* educational level open source electronics development tools<br />
<br />
* single buck/boost regulator, database of ones suitable for hobby prototype rework etc devices, as well as single devices easy enough for hobbyists to implement.<br />
* Programmable logic lab on a board. For hobby or educational use. Must have a website, extensive support info, and an active community, must be extremely cheap.<br />
* length of probes: Pomona small is too short, Pomona bigger one is OK or a bit too long<br />
* WTF idiotic documentation of digikey optical interrupters<br />
* doc diff bw flip flop and latch<br />
* Develop and market the tiniest embedded microprocessor. Count on about 4 (!!!) inputs and a 100kHz operation. for things like patching, hard logic replacement, hobby use, and human interface solutions (replaces things like 555, Toggle logic, etc)<br />
* my task consolidate absolutely all knowledge on amateur electronics into a single reference<br />
<br />
<br />
A website on how to connect real world inputs and outputs to digital circuits and microcontrollers<br />
<br />
* “generalize” every sensor category, and include information for people to learn to distinguish between different as well as same electronics.<br />
* fe, this will allow people to easily substitute or use another parts for microprocessor electronics.<br />
* an e-book/wiki on every piece of information to be able to interface to all types of electronics and sensors<br />
<br />
<br />
electronics for hobbyists: what is there to do for a hands-on electronics boys in the era of surface-mount and total integration?<br />
<br />
# new students/hobby/prototype service<br />
# get yourself with PI International for real projects for the third world<br />
# real colleges<br />
# competitions<br />
# home/local manufacturing technology<br />
# mod/create projects<br />
# great info sharing on products mods and feedback<br />
<br />
<br />
hobby fpga use:<br />
<br />
* make an online resource for hobby fpga use<br />
* hobby, low volume, prototyping, product replacement, education<br />
* open source non-project based software without arcane settings, tools, or options.<br />
* simplest, cheapest, smallest fpgas used<br />
* drag and drop and gui compilation only. absolutely no hand coding or compilation options specification<br />
* open source software, specifications, features, and tools. for example, automatically generate math acceleration for any c program.<br />
<br />
<br />
ElectronicsPortal.com<br />
<br />
* No product reviews<br />
* moves all of the different sites to one site<br />
* software<br />
* circuits by various authors<br />
* paid EEs to answer questions<br />
* grade 8-12, student, beginning EE oriented<br />
* "complete electronics lab" -- software package + boards + IO<br />
<br />
<br />
EEs of USA club<br />
<br />
* publishing<br />
* info<br />
* force colleges to remove shit courses<br />
* tells what to do<br />
* resources<br />
* ads<br />
* wanted<br />
* services<br />
<br />
<br />
about electronics repairs<br />
<br />
* most common problem for beginners is overthinking the process like digging into the boards without looking at the power supply, or blaming the relatively rugged electronics when a simple switch or mechanical problem is the likely cause, or a case on which the electronics depends on for operation.<br />
* write online about the actual easy steps to fix computers, electronics, as well as operating systems.<br />
<br />
<br />
digitizer i need: if not found, make and sell it myself<br />
<br />
* digital io<br />
* analog io<br />
* signal generator<br />
* spectrum analyzer<br />
* waveform generator<br />
* dmm (the most important option. if it does not replace a handheld dmm but is yet another instrument, then it is crap)<br />
<br />
* 1/2 channels max. anything more is too expensive and must be a separate module.<br />
* full open source full feature software suite<br />
* bandwidth is by application only. fe audio apps should have 200 kHz, etc. other ones like logging (10 kHz), embedded/robotics (100 MHz), etc<br />
* $200 maximum price. hobbyists and education will never pay something in the $500-2000 range.<br />
<br />
<br />
problems i encountered with electronics parts suppliers:<br />
<br />
* absolutely no pics in electronics catalogs. as always, when i do not know what i am looking for, it is impossible to find on the Internet<br />
* absolutely no flux suppliers<br />
* absolutely no water soluble information, suppliers, and pictures<br />
* no universally accessible part cross reference databases<br />
<br />
<br />
PI task: electronics<br />
<br />
* reparse all electronics books, circuits, etc and reorganize them into block circuits instead with comments on specific implementations for that particular function.<br />
* fe, a self-made metal detector would show a block circuit for one, and then the readers would use a computer or their brain to convert the blocks into discrete components.<br />
* preserve all old circuits for "how it was/could be done" information, while noting why it is no longer done that way anymore (fe, an almost fully digital metal detector instead of one with 4 transistors)<br />
* archive all circuits and books.<br />
* explain why things are not done some particular way any more.<br />
* maintain groups of people who actively build old circuits and parse old information with things such as tube and few-transistors based circuits.<br />
* move electronics to block-level thinking with few tweaks to standard blocks to suite a particular application.<br />
* show evolution of circuits for each minimal task.<br />
<br />
<br />
practical transistor knowledge ebook (hobby/technician)<br />
<br />
* No math, theory, bloated schematics, pencil/paper, etc<br />
* how to recognize circuit type at a glance<br />
* Minimum devices for switching application, amplifier, isolator, generator, etc<br />
* when to use bijunction and when to use mosfet<br />
* the only transistor part number you will need<br />
* software tools<br />
* simplify all circuits based on transistors by their type + supporting devices, and show how to do that yourself<br />
<br />
* review books (most are a mile wide and an inch deep). But the fail as references if a concept cannot be found in a single mile wide book<br />
* no emphasis on physical construction or the fact that devices fail, or how to repair electronics<br />
* how it operates, esp required conditions<br />
* BIGGEST FUCKING STUPIDITY: THE NIGHT BEFORE EXAM FACTOR: BOOK GOES ON AND ON ABOUT CRAP LIKE A PROFESSOR, BUT CRITICAL CONCEPTS ARE NOT EMPHASIZED, EXPLAINED, AND DEMONSTRATED<br />
* the only possible uses schematics by type<br />
* wird uses in circuit explained (lk base tied to emmiter thru a resistor for a two-wire device)<br />
* RL gotchas and examples from users<br />
* useable schematics books<br />
* how to buy transistors<br />
* explain negative polarity. Also how PNP can be used w neg ground<br />
* required forward bias<br />
<br />
<br />
wtf none of the circuits work?<br />
<br />
* Mosfet failed<br />
* photointerrupter failed<br />
* 5V regulator failed<br />
* basic stamp module failed<br />
* several logic ics failed<br />
* SR latch equivalent does not toggle LED (defective ic)<br />
* buffer did not work<br />
* SR latch toggled LEDs, but fails with mosfet or buffer (because logic high is only 4.5V)<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
===========================<br />
<br />
<br />
<br />
Q: What things can be asked on an interview to an electronics-related position (technician, assembly, etc)?<br />
<br />
<br />
<br />
A:<br />
<br />
* component identification<br />
* final inspection<br />
* esd standard<br />
* certificates<br />
* blueprint reading – steps, components, diagram<br />
* term for blueprint steps<br />
===========================<br />
<br />
<br />
<br />
External links<br />
* [http://en.wikipedia.org/wiki/Wikipedia:WikiProject_Electronics]</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1413
Buck Voltage Regulator Evaluation Project
2015-07-07T01:54:37Z
<p>Mkrdwiki: /* Circuit Features */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[Image:|thumb|'''Figure 5.1: System Level Diagram''']]<br />
<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1412
Buck Voltage Regulator Evaluation Project
2015-07-07T01:53:47Z
<p>Mkrdwiki: /* Detailed Design */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[Image:|thumb|'''Figure 5.1: System Level Diagram''']]<br />
<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 100mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1411
Buck Voltage Regulator Evaluation Project
2015-07-07T01:52:23Z
<p>Mkrdwiki: /* Inductor Re-Design */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[Image:|thumb|'''Figure 5.1: System Level Diagram''']]<br />
<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 500mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
TODO ADD<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1410
Buck Voltage Regulator Evaluation Project
2015-07-07T01:50:55Z
<p>Mkrdwiki: /* Appendix D – List of Printed Attachments */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[Image:|thumb|'''Figure 5.1: System Level Diagram''']]<br />
<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 500mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
<br />
L core loss at 100kHz?<br />
<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Document Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1409
Buck Voltage Regulator Evaluation Project
2015-07-07T01:50:24Z
<p>Mkrdwiki: /* Appendix D – List of Printed Attachments */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[Image:|thumb|'''Figure 5.1: System Level Diagram''']]<br />
<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 500mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
<br />
L core loss at 100kHz?<br />
<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Printed Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}</div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1408
Buck Voltage Regulator Evaluation Project
2015-07-07T01:49:20Z
<p>Mkrdwiki: /* Appendix A – Bill of Materials */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[Image:|thumb|'''Figure 5.1: System Level Diagram''']]<br />
<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 500mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
<br />
L core loss at 100kHz?<br />
<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Printed Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}<br />
D1 is not on BOM!<br />
<br />
<br />
[Slide] Load regulation specifies how much change occurs in the output voltage for a given range of load current values, usually from no load (NL) to full load (FL).<br />
<br />
<br />
Remarks from all datasheets<br />
<br />
<br />
Proj device average, peak ratings. Q C D L. Pd<br />
<br />
<br />
why highly necessary data not included in capacitor datasheet: Because it is critically value-specific. Use manufacturer's calculator tool. Or look up deviation by dielectric material type. <br />
<br />
<br />
wtf schematic is all fucked up in size: seemingly huge size, but tiny font???<br />
<br />
<br />
resistor in series with COUT electrolytic<br />
<br />
<br />
Digitize binder notes<br />
<br />
<br />
2M resistor across Ccomp2 to stabilize (reduce from 80dB) DC gain<br />
<br />
<br />
1ohm resistor in series with Cout electrolytic. HF ripple prevented from destroying capacitor, and short current. same for cin electrolytic. will limit inrush current on low impedance dc power supply connection. <br />
<br />
<br />
3-4uF ceramic capacitors in parallel at output (done)<br />
<br />
<br />
TIMA simulation would have SPICE models for TI components<br />
<br />
<br />
Need {capacitance, ESR} in relation to {voltage, frequency, ripple current, temperature}<br />
<br />
<br />
D2, at 2A, is entirely inappropriate for the design. Need a diode with rating of Vmax=Vsupply, Amax=Ashort+Aripple???<br />
<br />
<br />
app note for power MOSFETs<br />
<br />
<br />
snubber app note<br />
<br />
<br />
snubber reduces the power loss in the transistor<br />
<br />
reduce voltage and current stresses in the transistor<br />
<br />
<br />
Snubber provisional diode across top resistor<br />
<br />
<br />
SPICE sim with HS drive and synchronous rectification.<br />
<br />
<br />
Open Mode capacitors for input<br />
<br />
<br />
Wikipedia article on ceramic capacitors<br />
<br />
<br />
approximate “heatsink” thermal resistance based on PCB area<br />
<br />
<br />
FET gate drive magnitude with VCCX<br />
<br />
<br />
Transients, transient energy, and FFT at switch node<br />
<br />
<br />
Snubber must protect bottom MOSFET. Snubber and output filtering must protect vccx<br />
<br />
<br />
Open Mode capacitors. for input (exposed to outside voltages) capacitors<br />
<br />
Syfer 2220Y0630335KXT<br />
<br />
flexible termination.<br />
<br />
no sizes above 1210 due to bending issues, unless they are flex term.<br />
<br />
<br />
why Steve wants to eliminate all thru-hole parts from our products???<br />
<br />
<br />
an aluminum thru-hole input cap would relieve tension, and is not brittle like a ceramic.<br />
<br />
<br />
Remove RS power res from BOM, cost estimate<br />
<br />
<br />
Frequency and energy of transients<br />
<br />
<br />
re-do thermal photo with VCCX<br />
<br />
<br />
Dead time must be longer than reverse recovery time of sync fet<br />
<br />
Is my gate drive now 12v<br />
<br />
Open mode or flex term caps perpendicular to ea<br />
<br />
New dmm cal info<br />
<br />
Equipment serial numbers<br />
<br />
<br />
re-design summary:<br />
<br />
* cin aluminum<br />
* cout ceramic<br />
* snubber C R D<br />
* properly sized freewheeling diode<br />
* rsense<br />
<br />
Further improvement to report, only for my own benefit:<br />
<br />
* energy recovery snubber for buck converter<br />
<br />
<math>{\mathrm{\Theta }}_{\mathit{thermal}}=\frac{{T}_{\mathit{destination}}-{T}_{\mathit{source}}}{{P}_{D}}</math><br />
<br />
<br />
<math>{T}_{\mathit{junction}}={P}_{D}\ast \left({\mathrm{\Theta }}_{\mathit{total}}\right)+{T}_{\mathit{ambient}}</math><br />
<br />
<br />
<br />
<br />
----<br />
<references/></div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1407
Buck Voltage Regulator Evaluation Project
2015-07-07T01:48:02Z
<p>Mkrdwiki: /* References */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[Image:|thumb|'''Figure 5.1: System Level Diagram''']]<br />
<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 500mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
<br />
L core loss at 100kHz?<br />
<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[http://webench.ti.com/ Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
<br />
Total developmental cost<br />
<br />
Add COUT ceramic caps<br />
<br />
Correct BOM errors<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Printed Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}<br />
D1 is not on BOM!<br />
<br />
<br />
[Slide] Load regulation specifies how much change occurs in the output voltage for a given range of load current values, usually from no load (NL) to full load (FL).<br />
<br />
<br />
Remarks from all datasheets<br />
<br />
<br />
Proj device average, peak ratings. Q C D L. Pd<br />
<br />
<br />
why highly necessary data not included in capacitor datasheet: Because it is critically value-specific. Use manufacturer's calculator tool. Or look up deviation by dielectric material type. <br />
<br />
<br />
wtf schematic is all fucked up in size: seemingly huge size, but tiny font???<br />
<br />
<br />
resistor in series with COUT electrolytic<br />
<br />
<br />
Digitize binder notes<br />
<br />
<br />
2M resistor across Ccomp2 to stabilize (reduce from 80dB) DC gain<br />
<br />
<br />
1ohm resistor in series with Cout electrolytic. HF ripple prevented from destroying capacitor, and short current. same for cin electrolytic. will limit inrush current on low impedance dc power supply connection. <br />
<br />
<br />
3-4uF ceramic capacitors in parallel at output (done)<br />
<br />
<br />
TIMA simulation would have SPICE models for TI components<br />
<br />
<br />
Need {capacitance, ESR} in relation to {voltage, frequency, ripple current, temperature}<br />
<br />
<br />
D2, at 2A, is entirely inappropriate for the design. Need a diode with rating of Vmax=Vsupply, Amax=Ashort+Aripple???<br />
<br />
<br />
app note for power MOSFETs<br />
<br />
<br />
snubber app note<br />
<br />
<br />
snubber reduces the power loss in the transistor<br />
<br />
reduce voltage and current stresses in the transistor<br />
<br />
<br />
Snubber provisional diode across top resistor<br />
<br />
<br />
SPICE sim with HS drive and synchronous rectification.<br />
<br />
<br />
Open Mode capacitors for input<br />
<br />
<br />
Wikipedia article on ceramic capacitors<br />
<br />
<br />
approximate “heatsink” thermal resistance based on PCB area<br />
<br />
<br />
FET gate drive magnitude with VCCX<br />
<br />
<br />
Transients, transient energy, and FFT at switch node<br />
<br />
<br />
Snubber must protect bottom MOSFET. Snubber and output filtering must protect vccx<br />
<br />
<br />
Open Mode capacitors. for input (exposed to outside voltages) capacitors<br />
<br />
Syfer 2220Y0630335KXT<br />
<br />
flexible termination.<br />
<br />
no sizes above 1210 due to bending issues, unless they are flex term.<br />
<br />
<br />
why Steve wants to eliminate all thru-hole parts from our products???<br />
<br />
<br />
an aluminum thru-hole input cap would relieve tension, and is not brittle like a ceramic.<br />
<br />
<br />
Remove RS power res from BOM, cost estimate<br />
<br />
<br />
Frequency and energy of transients<br />
<br />
<br />
re-do thermal photo with VCCX<br />
<br />
<br />
Dead time must be longer than reverse recovery time of sync fet<br />
<br />
Is my gate drive now 12v<br />
<br />
Open mode or flex term caps perpendicular to ea<br />
<br />
New dmm cal info<br />
<br />
Equipment serial numbers<br />
<br />
<br />
re-design summary:<br />
<br />
* cin aluminum<br />
* cout ceramic<br />
* snubber C R D<br />
* properly sized freewheeling diode<br />
* rsense<br />
<br />
Further improvement to report, only for my own benefit:<br />
<br />
* energy recovery snubber for buck converter<br />
<br />
<math>{\mathrm{\Theta }}_{\mathit{thermal}}=\frac{{T}_{\mathit{destination}}-{T}_{\mathit{source}}}{{P}_{D}}</math><br />
<br />
<br />
<math>{T}_{\mathit{junction}}={P}_{D}\ast \left({\mathrm{\Theta }}_{\mathit{total}}\right)+{T}_{\mathit{ambient}}</math><br />
<br />
<br />
<br />
<br />
----<br />
<references/></div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1406
Buck Voltage Regulator Evaluation Project
2015-07-07T01:47:40Z
<p>Mkrdwiki: /* References */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[Image:|thumb|'''Figure 5.1: System Level Diagram''']]<br />
<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 500mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
<br />
L core loss at 100kHz?<br />
<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
<br />
<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
<br />
Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
<br />
<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
<br />
<br />
[webench.ti.com Texas Instruments (TI) Webench]<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
<br />
Total developmental cost<br />
<br />
Add COUT ceramic caps<br />
<br />
Correct BOM errors<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix D – List of Printed Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}<br />
D1 is not on BOM!<br />
<br />
<br />
[Slide] Load regulation specifies how much change occurs in the output voltage for a given range of load current values, usually from no load (NL) to full load (FL).<br />
<br />
<br />
Remarks from all datasheets<br />
<br />
<br />
Proj device average, peak ratings. Q C D L. Pd<br />
<br />
<br />
why highly necessary data not included in capacitor datasheet: Because it is critically value-specific. Use manufacturer's calculator tool. Or look up deviation by dielectric material type. <br />
<br />
<br />
wtf schematic is all fucked up in size: seemingly huge size, but tiny font???<br />
<br />
<br />
resistor in series with COUT electrolytic<br />
<br />
<br />
Digitize binder notes<br />
<br />
<br />
2M resistor across Ccomp2 to stabilize (reduce from 80dB) DC gain<br />
<br />
<br />
1ohm resistor in series with Cout electrolytic. HF ripple prevented from destroying capacitor, and short current. same for cin electrolytic. will limit inrush current on low impedance dc power supply connection. <br />
<br />
<br />
3-4uF ceramic capacitors in parallel at output (done)<br />
<br />
<br />
TIMA simulation would have SPICE models for TI components<br />
<br />
<br />
Need {capacitance, ESR} in relation to {voltage, frequency, ripple current, temperature}<br />
<br />
<br />
D2, at 2A, is entirely inappropriate for the design. Need a diode with rating of Vmax=Vsupply, Amax=Ashort+Aripple???<br />
<br />
<br />
app note for power MOSFETs<br />
<br />
<br />
snubber app note<br />
<br />
<br />
snubber reduces the power loss in the transistor<br />
<br />
reduce voltage and current stresses in the transistor<br />
<br />
<br />
Snubber provisional diode across top resistor<br />
<br />
<br />
SPICE sim with HS drive and synchronous rectification.<br />
<br />
<br />
Open Mode capacitors for input<br />
<br />
<br />
Wikipedia article on ceramic capacitors<br />
<br />
<br />
approximate “heatsink” thermal resistance based on PCB area<br />
<br />
<br />
FET gate drive magnitude with VCCX<br />
<br />
<br />
Transients, transient energy, and FFT at switch node<br />
<br />
<br />
Snubber must protect bottom MOSFET. Snubber and output filtering must protect vccx<br />
<br />
<br />
Open Mode capacitors. for input (exposed to outside voltages) capacitors<br />
<br />
Syfer 2220Y0630335KXT<br />
<br />
flexible termination.<br />
<br />
no sizes above 1210 due to bending issues, unless they are flex term.<br />
<br />
<br />
why Steve wants to eliminate all thru-hole parts from our products???<br />
<br />
<br />
an aluminum thru-hole input cap would relieve tension, and is not brittle like a ceramic.<br />
<br />
<br />
Remove RS power res from BOM, cost estimate<br />
<br />
<br />
Frequency and energy of transients<br />
<br />
<br />
re-do thermal photo with VCCX<br />
<br />
<br />
Dead time must be longer than reverse recovery time of sync fet<br />
<br />
Is my gate drive now 12v<br />
<br />
Open mode or flex term caps perpendicular to ea<br />
<br />
New dmm cal info<br />
<br />
Equipment serial numbers<br />
<br />
<br />
re-design summary:<br />
<br />
* cin aluminum<br />
* cout ceramic<br />
* snubber C R D<br />
* properly sized freewheeling diode<br />
* rsense<br />
<br />
Further improvement to report, only for my own benefit:<br />
<br />
* energy recovery snubber for buck converter<br />
<br />
<math>{\mathrm{\Theta }}_{\mathit{thermal}}=\frac{{T}_{\mathit{destination}}-{T}_{\mathit{source}}}{{P}_{D}}</math><br />
<br />
<br />
<math>{T}_{\mathit{junction}}={P}_{D}\ast \left({\mathrm{\Theta }}_{\mathit{total}}\right)+{T}_{\mathit{ambient}}</math><br />
<br />
<br />
<br />
<br />
----<br />
<references/></div>
Mkrdwiki
http://www.wiki.mkrd.info/index.php?title=Buck_Voltage_Regulator_Evaluation_Project&diff=1405
Buck Voltage Regulator Evaluation Project
2015-07-07T01:45:57Z
<p>Mkrdwiki: /* System Level Design */</p>
<hr />
<div>'''''Abstract: This project demonstrates design and testing of a DC-DC Buck Topology, Synchronous Rectification Voltage Regulator. Emphasis of regulator design is on low output ripple, high efficiency, and high reliability. These requirements would be ideal for a Solar Panel Array or a Rechargeable Battery (secondary storage) Array.'''''<br />
<br />
Initial design stage used Texas Instruments Webench online design tool, and a TI Evaluation Board.<br />
<br />
Project requirements were 48VDC in, 12VDC at 10A out.<br />
<br />
<br />
<br />
= Disclaimer =<br />
<br />
THIS ARTICLE IS NOT AUTHORIZED FOR RE-DISTRIBUTION, RE-TRANSMISSION, OR REPRODUCTION.<br />
<br />
ANY INFORMATION CONTAINED IN THIS ARTICLE MAY ONLY BE USED FOR NON-COMMERCIAL PURPOSES ONLY.<br />
<br />
ALL INFORMATION IS “FOR REFERENCE ONLY”.<br />
<br />
COPYRIGHT © 2015 HTTP://WWW.MKRD.INFO/<br />
<br />
REPORT VIOLATIONS OF THIS POLICY, FOR A REWARD, TO E-MAIL ADDRESS BELOW.<br />
<br />
AUTHOR CONTACT INFORMATION:<br />
<br />
ADMINISTRATOR, <br />
<br />
[[User:Mkrdwiki|Mkrdwiki]] ([[User talk:Mkrdwiki|talk]])<br />
<br />
= Listing of Acronyms =<br />
BOM – Bill of Materials<br />
<br />
DC – Direct Current<br />
<br />
DCR – DC Resistance (Inductor)<br />
<br />
ESR – Equivalent Series Resistance<br />
<br />
FN – Flat, No leads device package<br />
<br />
IC – Integrated Circuit<br />
<br />
LDO – Low-Dropout Regulator<br />
<br />
MOSFET – Metal Oxide Semiconductor Field Effect Transistor<br />
<br />
PCB – Printed Circuit Board<br />
<br />
PMIC – Power Management Integrated Circuit<br />
<br />
PUT – Power-Up Test<br />
<br />
RMS – Root Mean Square<br />
<br />
SMD – Surface Mount Design, Surface Mount Device<br />
<br />
TI – Texas Instruments<br />
<br />
UVLO – Under-Voltage Lock-Out<br />
<br />
= Project Design Requirements =<br />
The objective of this Project is to design, construct, and test a DC-DC voltage regulator with buck topology and synchronous rectification (“Voltage Regulator”).<br />
<br />
Input to Voltage Regulator shall be a nominally 48V input. <br />
<br />
Output from Voltage Regulator shall be a nominal 12V.<br />
<br />
Output current capability of Voltage Regulator (constant-ON operation) shall be 10A.<br />
<br />
Voltage Regulator shall current limit maximum output to 15A. Voltage regulator shall tolerate permanent short circuit condition at its output, and may either maintain a 15A output current, or enter a shutdown after a period of time of short-current condition.<br />
<br />
Voltage regulator shall tolerate input voltage variation of ±10%.<br />
<br />
Output voltage regulation shall be ±1% at 50% load.<br />
<br />
Output ripple shall be less than 100mV.<br />
<br />
Voltage Regulator shall not draw excessive ripple current from its input.<br />
<br />
Voltage Regulator shall be a high-reliability design to protect the input from damage (e.g. from a short circuit within the Voltage Regulator). <br />
<br />
Voltage Regulator shall be a long-life design, to last for the life of e.g. Solar Panel Array (10 years effective life). <br />
<br />
Voltage Regulator output accuracy and precision will be limited by issues discussed in <u>Tolerance Stacking</u>.<br />
<br />
= Project Design =<br />
== System Level Design ==<br />
Expected inputs to this Regulator e.g. solar panels and rechargeable batteries produce an output voltage which varies with the amount of incident solar radiation or chemical charge remaining. Therefore, the Voltage Regulator shall [Requirement] be able to provide a constant output voltage with varying input voltage (voltage regulation). Given the complexity of switching-mode operation, voltage regulation, and synchronous rectification, a controller IC will be used in this project. <br />
<br />
<br />
Given the high output current requirement (10A), and the subject matter of the Project, discrete power MOSFETs shall be used as circuit switching and rectification elements. <br />
<br />
<br />
As this was a time-sensitive Project, Texas Instruments (TI) Webench passive part calculations, choices, and BOM will be used along with a pre-made Printed Circuit Board (PCB). This choice will make it easy for hobbyists, tinkerers, DIY'ers, and students to follow material of this article.<br />
<br />
<br />
Project shall demonstrate:<br />
<br />
* Knowledge of DC-DC regulator design<br />
* Circuit operation<br />
* Functionality of Power Electronics components of circuit<br />
* Ability of author and reader to test DC-DC regulator for proper operation<br />
<br />
For the purposes of project evaluation, circuit shall be supplied by a 48VDC regulated power supply, and output shall be loaded with a resistive load or an active load (bank of MOSFETs).<br />
<br />
<br />
Conformal coating shall be used to avoid electric shock to human operator, and to prevent damage due to moisture.<br />
<br />
== System Level Diagram ==<br />
<u>Figure 5.1: System Level Diagram</u> is a System Level Diagram of the Voltage Regulator. <br />
<br />
<br />
[[Image:|thumb|'''Figure 5.1: System Level Diagram''']]<br />
<br />
<br />
== Design Aids ==<br />
=== Online Design Tool ===<br />
Texas Instruments has a Webench Online Design Tool. Chosen IC controller (see <u>7.2.4</u> <u>Integrated Circuit (IC) Controller</u>) is covered by Webench. Webench will be used to derive most of necessary circuit components calculations. Then, critical components (MOSFETs, inductor, output filtering capacitor) values will be verified by hand. Webench suggested components and PCB will be purchased. Received parts will be soldered onto the PCB. The design will then be tested. <br />
<br />
<br />
== Schematic ==<br />
Webench has produced the following schematic (<u>Figure 5.2: Webench Schematic</u>) for requirements of 48Vin, 12Vout, 10Aout, LM5116:<br />
<br />
<br />
[[Image:|thumb|'''Figure 5.2: Webench Schematic''']]<br />
<br />
<br />
== Circuit Features ==<br />
The LM5116 controller has the following built-in features:<br />
<br />
<br />
* Current Mode Control (Emulated Current Ramp), Emulated Peak Current Mode<br />
* Wide Operating Range Up to 100V<br />
* Variable Frequency (50 kHz to 1 MHz)<br />
* Shutdown / Enable Input<br />
* Settable Output from 1.215V to 80V<br />
* Programmable Current Limit<br />
* Programmable Soft-Start<br />
* Programmable Line Under-Voltage lockout<br />
* Thermal Shutdown<br />
* Adaptive Dead-time Control<br />
<br />
== Planned Project Timeline ==<br />
Planned Project Timeline is outlined below:<br />
<br />
# Project Specification<br />
# Selection of IC controller<br />
# Webench Design<br />
# Purchasing of Webench recommended components and PCB<br />
# PCB Assembly<br />
# Regulator Testing<br />
# Justification of all Webench Calculations, per component datasheets<br />
# Re-Design Suggestions<br />
<br />
= Applicable Industry Standards =<br />
Below is a listing of <u>Table 6.1: Project Applicable Industry Standards</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Standard'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Title'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Remarks'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD-001</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Requirements for Soldered Electrical and Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-600</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Printed Boards</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-A-610</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Acceptability of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>IPC-7711/7721</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Rework, Repair and Modification of Electronic Assemblies</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Applies to project hand-assembled board</center><br />
<br />
|}<br />
'''Table 6.1: Project Applicable Industry Standards'''<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Detailed Design =<br />
First design iteration will use component values suggested by TI Webench because speed of placement of shipment was ''critical'' to success of this project. <br />
<br />
<br />
Webench has optimized between size, cost, and weight of components (slow switching frequency) and power loss (dissipation) (high switching frequency) for a frequency of ~100kHz.<br />
<br />
<br />
Project design is for a maximum of 500mV output voltage ripple. <br />
<br />
<br />
''After'' an order was placed for Webench suggested components and PCB, calculations below were made to qualify design for target application. Any issues found with Webench design, and any areas for improvement will be documented in a later section (<u>9</u> <u>Design Improvements</u>).<br />
<br />
<br />
== Individual Mechanical Components Choices ==<br />
=== MOSFET heatsinks ===<br />
PCB uses thermal via technology to dissipate heat from device into the PCB plane. Due to low heat loss in active devices and use of thermal vias, heatsinks are not required. <br />
<br />
<br />
=== Printed Circuit Board ===<br />
This project uses a pre-designed and pre-built PCB. An online product listing PCB is shown in <u>Figure 7.1: Online product listing PCB</u>. <br />
<br />
<br />
[[Image:|thumb|'''Figure 7.1: Online product listing PCB''']]<br />
<br />
<br />
== Individual Electronic Components Choices ==<br />
Unless otherwise specified, all electronic parts shall be Surface Mount Design (SMD) mounting technology.<br />
<br />
<br />
Only the following major components choices will be described here in detail, leaving the rest to Webench and datasheet calculations:<br />
<br />
* IC Regulator<br />
* Active Switch MOSFET<br />
* Synchronous Rectifier MOSFET<br />
* Input Protection Fuse<br />
* Inductor<br />
* Input Filtering Capacitors<br />
* Output Filtering Capacitors<br />
<br />
=== Duty Cycle ===<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{{V}_{\text{IN}}}{{V}_{\mathit{OUT}}}=\frac{12}{48}=0.25=25\text{\%}</math></center><br />
! <div align="right">(7.1)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Output Voltage Ripple ===<br />
The output ripple is determined by inductor ripple current and output capacitor capacitance and ESR. <br />
<br />
<br />
Output voltage ripple due to inductor ripple can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}=\frac{48\ast 0.25\ast \left(1-0.25\right)}{8\ast 22\mathrm{\mu }\ast 560\mathrm{\mu }\ast 100{k}^{2}}=9\mathit{mV}</math></center><br />
! <div align="right">(7.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Webench specified capacitor has an ESR rating of 14mΩ (at what setup?). This ESR will cause a voltage fluctuation in the amount of <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{V}_{O\left(\mathit{ESR}\right)}=\mathrm{\Delta }{i}_{C}\ast {r}_{C}=4.09\ast 14m=57.26\mathit{mV}</math></center><br />
! <div align="right">(7.3)</div><br />
<br />
|-<br />
<br />
|}<br />
However, the experimentally measured value (see <u>Output Voltage Ripple</u>) was 760mV. Calculations do not agree to empirical data because ESR of Webench suggested electrolytic capacitor at switching frequency is not considered. <br />
<br />
<br />
=== Tolerance Stacking ===<br />
Project tolerance stacking - two 1% resistors. IC spec. Ripple. 5% expected.<br />
<br />
<br />
Difference between Accuracy (ability to output specified voltage) and Precision (output ripple effects). <br />
<br />
<br />
=== Integrated Circuit (IC) Controller ===<br />
A Digi-Key ([http://www.Digi-Key.com/ http://www.Digi-Key.com/]) search was performed for the “Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers” category, as the Regulator, since a discrete external MOSFET's will be used. <br />
<br />
<br />
Available IC's were narrowed down by the following criteria:<br />
<br />
* In Stock: Yes<br />
* Number of Outputs: 1<br />
* Topology: Buck Only<br />
* Voltage – Supply: >48V<br />
* Packaging: Not Digi-Reel<br />
* Package / Case: Not “FN” (flat, no leads)<br />
<br />
The Surface Mount Device (SMD) Exposed Pad allows larger heat dissipation, but part is not removable using conventional manual soldering rework processes. As this is a time-sensitive project, and part removal and / or replacement is expected, Exposed Pad technology will not be utilized for this Project (pad will be left unsoldered).<br />
<br />
<br />
FN (flat, no leads) package types has been rejected for same reasoning as above. <br />
<br />
<br />
Further narrowing down to controllers which support synchronous rectification leaves devices by Linear Technology and Texas Instruments.<br />
<br />
<br />
The only device remaining which is supported by TI Webench is the LM5116. Chosen part type:<br />
<br />
Texas InstrumentsLM5116MHX/NOPBSMD<br />
<br />
<br />
=== Inductor ===<br />
At output current of 10A at 12V, output equivalent resistance is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>R=\frac{V}{I}=\frac{12}{10}=1.2\mathrm{\Omega }</math></center><br />
! <div align="right">(7.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor critical value for continuous current operation can be found from <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{L}_{\mathit{crit}}=\frac{\left(1-D\right)\ast R}{2\ast f}=\frac{\left(1-0.25\right)\ast 1.2}{2\ast 100k}=4.5\mathrm{\mu }H</math></center><br />
! <div align="right">(7.5)</div><br />
<br />
|-<br />
<br />
|}<br />
However, with this inductance value, ripple current thru inductor will be<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta I}}_{L}=\frac{{V}_{O}\ast \left({V}_{S}-{V}_{O}\right)}{f\ast L\ast {V}_{S}}=\frac{12\ast \left(48-12\right)}{100k\ast 4.5\mathrm{\mu }\ast 48}=20A</math></center><br />
! <div align="right">(7.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Too large of a current for a reasonable inductor. Furthermore, this 20A ripple current will be passed to the output filtering capacitor C<sub>O</sub>, necessitating an unreasonably large capacitance and an unreasonably low ESR. <br />
<br />
<br />
TI Webench uses a design choice of inductor ripple being 40% of output current, a much more reasonable value. Substituting<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathrm{\Delta }{I}_{L}=0.4\ast {I}_{O}=0.4\ast 10=4A</math></center><br />
! <div align="right">(7.7)</div><br />
<br />
|-<br />
<br />
|}<br />
<u>(7.7)</u> into <u>(7.6)</u> results in L = 22.5μH. <br />
<br />
<br />
When switching is active, current thru inductor goes up to a maximum of<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{Lmax}}={V}_{O}\ast \left\lbrack \frac{1}{R}+\frac{1-D}{2\ast L\ast f}\right\rbrack =12\ast \left\lbrack \frac{1}{1.2}+\frac{1-0.25}{2\ast 22\mathrm{\mu }\ast 100k}\right\rbrack =12.05A</math></center><br />
! <div align="right">(7.8)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor must be rated for this saturation current, or higher.<br />
<br />
<br />
Inductor RMS current is:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{RMS}=\sqrt{{I}_{L},{\mathit{avg}}^{2}+{\left\lbrack \left(\frac{\frac{\mathrm{\Delta }{i}_{L}}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=\sqrt{{10}^{2}+{\left\lbrack \left(\frac{\frac{4.09}{2}}{\sqrt{\left(3\right)}}\right)\right\rbrack }^{2}}=10.07A</math></center><br />
! <div align="right">(7.9)</div><br />
<br />
|-<br />
<br />
|}<br />
where average inductor current is<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{L},\mathit{avg}={I}_{O}={I}_{R\left(L\right)}</math></center><br />
! <div align="right">(7.10)</div><br />
<br />
|-<br />
<br />
|}<br />
Inductor wire must be rated for the RMS current. However, the lower inductor DCR is, the lower the losses will be in the circuit.<br />
<br />
<br />
For L1 re-design, see <u>9.11</u> <u>Inductor Re-Design</u>.<br />
<br />
<br />
Webench has chosen the following component:<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Inductance</center><br />
! <center>IRMS</center><br />
! <center>DCR</center><br />
! <center>Saturation current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Coilcraft, Inc</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>SER2918H-223KL</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Ferrite</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>22μH</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>20A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>12.0A (-10%)</center><br />
<br />
|}<br />
'''Table 7.1: Inductor, Webench'''<br />
<br />
<br />
=== Input Protection Fuse ===<br />
An inline fuse-holder and a fuse shall be used for protection of power supply feeding this circuit. Circuit current requirements at full output, the worst input voltage, and worst estimate of 80% efficiency will be <u>(7.11)</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\frac{\frac{\left(12\ast 10\right)}{48-0.1\ast 48}}{0.8}=3.47A</math></center><br />
! <div align="right">(7.11)</div><br />
<br />
|-<br />
<br />
|}<br />
A slow-blow fuse of 3.5A shall be used at circuit input due to Input Filtering Capacitors (<u>7.2.8</u> <u>Input Filtering Capacitors</u>). <br />
<br />
<br />
=== Output Filtering Capacitors ===<br />
Project target is 100mV of ripple at rated current. <br />
<br />
<br />
Required output capacitance can be found from:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{\mathit{\Delta V}}_{C}=\frac{{V}_{S}\ast D\ast \left(1-D\right)}{8\ast L\ast C\ast {f}^{2}}</math></center><br />
! <div align="right">(7.12)</div><br />
<br />
|-<br />
<br />
|}<br />
For ΔV<sub>C</sub> of 100mV, formula asks for C<sub>O</sub><nowiki>=51.1</nowiki>μF. This does not agree with empirical data when ESR of practical capacitors at Regulator switching frequency is considered (see <u>Output Voltage Ripple</u>) of 760mV of ripple for 560μF of electrolytic output capacitance. <br />
<br />
<br />
Webench has selected an SMD capacitor with specifications:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Manufacturer</center><br />
! <center>Part Number</center><br />
! <center>Type</center><br />
! <center>Capacitance</center><br />
! <center>Voltage Rating</center><br />
! <center>ESR at fSW</center><br />
! <center>Maximum ripple current</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Panasonic Electronic Components</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16SVPF560M</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Polymer</center><br />
| style="background-color:transparent;border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>560μF</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>16V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>14mΩ</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>???</center><br />
<br />
|}<br />
'''Table 7.2: Output Filtering Capacitor, Webench'''<br />
<br />
<br />
It is standard industry practice to connect several capacitors in parallel to reduce equivalent ESR. If output capacitance or ESR is found inadequate, then supplemental capacitors will be connected in parallel. <br />
<br />
<br />
The 16V capacitor voltage rating as suggested by Webench below industry standard safety margin of 1.5X and is too low. Future design iterations shall use 20-25V rated capacitors on the output.<br />
<br />
<br />
=== Input Filtering Capacitors ===<br />
Input capacitance 3X 10UF 100V 20% X7S. Dielectric de-rating capacitance at 48V?<br />
<br />
<br />
Additional input output capacitors? Additional output capacitors?<br />
<br />
<br />
=== MOSFET Switch ===<br />
Calculation.<br />
<br />
<br />
=== MOSFET Active Rectifier ===<br />
Calculation.<br />
<br />
Required to pass all current.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. Diode type should be a Schottky, for improved switching. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Verify below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{AVG}}={I}_{O}\endash {I}_{\text{IN}}=10\endash 2.78=7.22A</math></center><br />
! <div align="right">(7.13)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>I\left(\mathit{peak}\right)={I}_{L}\left(\mathit{peak}\right)=12.05A</math></center><br />
! <div align="right">(7.14)</div><br />
<br />
|-<br />
<br />
|}<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{T}_{\mathit{ON}}={T}_{\mathit{total}}\ast D=\frac{1}{f}\ast D=\frac{1}{100k}\ast 0.25=2.5\mathrm{\mu }s</math></center><br />
! <div align="right">(7.15)</div><br />
<br />
|-<br />
<br />
|}<br />
MOSFET switching speed should be 1/10, or 0.25μs for low switching loss. <br />
<br />
<br />
== PCB Protection ==<br />
Due to high voltage present, PCB shall have applied shielding to protect a human operator against shock. Conformal coating can shield against shock, and also protect PCB from moisture. <br />
<br />
<br />
If used outdoors, PCB shall be placed in a shielded enclosure, and shall avoid direct incident sunlight. <br />
<br />
<br />
== Circuit Simulation ==<br />
Simplified functional circuit simulation was performed with LTSPICE. <br />
<br />
<br />
SPICE synchronous circuit simulation. Use available textbook files. Compare to scope shots of my circuit. <br />
<br />
<br />
Simulation:Overly simplistic not applicableThorough requires models for all major circuit components<br />
<br />
<br />
TINA 129 USD<br />
<br />
<br />
= Testing Methodology and Test Results =<br />
== Test Measurements ==<br />
The following measurements shall be obtained of circuit operation:<br />
<br />
<br />
* Operating frequency<br />
* Circuit duty cycle for full-load operation<br />
* Output voltage ripple<br />
* Waveforms for major circuit components<br />
* Gate control voltage for both MOSFETs<br />
* Circuit efficiency at full load<br />
* Turn-ON settling time (into full load)<br />
* No-load output voltage<br />
* Full-load output voltage<br />
* Output voltage for 25, 50% of load current<br />
* Minimum input voltage for ±0.5V output voltage regulation<br />
* Sense Resistor current waveform (representative of inductor current waveform)<br />
* Short-circuit behavior<br />
* Control loop voltage waveform<br />
<br />
Transient Response Testing:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
In addition, a thermal infra-red image of PCB shall be obtained with circuit supplying full load current for 30 minutes with no forced airflow. <br />
<br />
<br />
== Test Requirements ==<br />
Voltage Regulator shall PASS the following tests:<br />
<br />
<br />
* Operation with input voltage variation of ±10%, no load and full load<br />
* Output voltage ripple less than 50mV at full load<br />
* Output voltage regulation ≤1% from no load to full load<br />
* Short circuit test (output current shall limit itself to 15A)<br />
<br />
== Test Procedure ==<br />
<u>Table 8.1: Project Test Procedure</u> below summarizes work which was performed to design, assemble, and test the Regulator. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Procedure Step</center><br />
! <center>Results</center><br />
! <center>Remarks</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Obtain Project Requirements</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial Design Stage</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Received PCB & Parts Verification</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Issues found with BOM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>See Engineering Notebook</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB Assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>J-STD Class I Assembled PCB Inspection</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Workmanship acceptable</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Power-Up Test (PUT)</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Voltage Regulator Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Completed</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Re-design needed</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Transient Testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Test Equipment Not Available</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Re-Design, Re-Test</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>In Progress</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Report Close-Out</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Awaiting previous steps</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|}<br />
'''Table 8.1: Project Test Procedure'''<br />
<br />
<br />
== PCB Assembly ==<br />
Regulator PCB was assembled and soldered by hand to IPC J-STD Class I specifications. Results are shown below in <u>Figure 8.1: Assembled PCB, Top</u> and <u>Figure 8.2: Assembled PCB, Bottom</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.1: Assembled PCB, Top''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.2: Assembled PCB, Bottom''']]<br />
<br />
<br />
Rubber feet were added to bottom of PCB for high-voltage isolation, prevention of damage to PCB, and marginal heat dissipation improvement.<br />
<br />
<br />
== Test Results ==<br />
=== Test Setup ===<br />
Test setup, showing major test components used, is shown below in <u>Figure 8.3: Test Setup</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.3: Test Setup''']]<br />
<br />
<br />
=== Test Equipment Calibration Information ===<br />
The following calibrated test equipment was used to obtain test measurements:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Make</center><br />
! <center>Model</center><br />
! <center>Equipment Type</center><br />
! <center>Calibration Facility</center><br />
! <center>Calibration ID</center><br />
<br />
<center>Serial Number</center><br />
! <center>Expiration Date</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1925</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>23Apr2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C0499</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>11May2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hewlett Packard</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>34401A</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Bench-top DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3791</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30May2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Fluke</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>83V</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Hand-held DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C2456</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>09Dec2015</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DPO4054</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Oscilloscope, 500MHz</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>C1888</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>25Mar2016</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>new DMM</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Megger</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>DLRO 10X</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Milliom-meter</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Tektronix</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>611-429/051005/2481</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>27Oct2015</center><br />
<br />
|}<br />
'''Table 8.2: Equipment Calibration Information'''<br />
<br />
<br />
=== Power-Up Testing (PUT) ===<br />
The following procedure was used for safe Power-Up Testing of the Regulator:<br />
<br />
<br />
A bench power supply was set to 24V with 0.1A limit. When Regulator was connected to this power supply, no output voltage was produced, and input current draw was 0.03A. This is due to the Under-Voltage Lock-Out (UVLO) feature of the circuit.<br />
<br />
<br />
Power supply voltage was then slowly increased. Regulator turned ON (started to produce output voltage) at 37.5V. Input current draw was 0.05A (no Regulator load), and Regulator no-load output voltage was 12.07V. <br />
<br />
<br />
To test no-load ±10% input voltage deviation, power supply was varied as shown below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Power Supply Voltage, V</center><br />
! <center>Regulator Output Voltage, V</center><br />
! <center>Regulator Input Current Draw, A</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.05</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.07</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>0.07</center><br />
<br />
|}<br />
'''Table 8.3: No-Load Input Voltage Variation'''<br />
<br />
<br />
Regulator shows it can tolerate ±10% input voltage deviation, and also shows excellent output voltage no-load stability. <br />
<br />
<br />
Intermediate load operation was tested next. Power supply was set to 48V, 3.1A current limit. <br />
<br />
<br />
Regulator showed the following results when loaded with intermediate resistance values:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Load Resistance, Ω'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Regulator Voltage Output, V'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Regulator Current Output, A'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>2.275</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.05</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>5.224</center><br />
<br />
|}<br />
'''Table 8.4: Intermediate Loads'''<br />
<br />
<br />
Regulator is showing excellent output voltage stability at 50% load. <br />
<br />
<br />
Circuit efficiency at 50% load was calculated below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Voltage, V'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Current, A'''</center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Power, W'''</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>48.308</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>0.968</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>46.7621</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.06</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3.660</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>44.1396</center><br />
<br />
|}<br />
'''Table 8.5: 50% Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{46.7621-44.1396}{46.7621}=0.944=94.4\text{\%}</math></center><br />
! <div align="right">(8.1)</div><br />
<br />
|-<br />
<br />
|}<br />
A 5.61% fraction (2.623W) of input power was dissipated as heat inside the Regulator. Such amount of heat should not necessitate forced air or a heatsink for dissipation.<br />
<br />
<br />
=== Full-Load Testing ===<br />
A low-resistance, high dissipation rating variable resistor was used as a load for Full-Load Testing. At the output current of 9.94A, Regulator output was 11.999V. This shows excellent regulation of output voltage from “no load” to “full load” of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Regulation}=\frac{{V}_{O}\mathit{no}\mathit{load}-{V}_{O}\mathit{full}\mathit{load}}{{V}_{O}\mathit{no}\mathit{load}}=\frac{12.07-11.999}{11.999}=0.592\text{\%}</math></center><br />
! <div align="right">(8.2)</div><br />
<br />
|-<br />
<br />
|}<br />
Full-load efficiency was calculated from measurements below:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <br />
! <center>Voltage, V</center><br />
! <center>Current, A</center><br />
! <center>Power, W</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Input'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>46.504</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.6780</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>124.538</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Output'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>11.997</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>9.93</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>119.13</center><br />
<br />
|}<br />
'''Table 8.6: Full-Load Efficiency'''<br />
<br />
<br />
Circuit efficiency can be calculated as follows:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>\mathit{Efficiency}=1-\frac{{P}_{\text{IN}}-{P}_{\mathit{OUT}}}{{P}_{\text{IN}}}=1-\frac{124.538-119.13}{124.538}=0.957=95.7\text{\%}</math></center><br />
! <div align="right">(8.3)</div><br />
<br />
|-<br />
<br />
|}<br />
A 4.34% fraction (5.408W) of input power was dissipated as heat inside the Regulator. Thermal infra-red images of Regulator have been taken (see <u>Thermal Infra-Red Imaging Of Full-Load Operation</u>) to judge whether heat dissipation is adequate to keep highest component temperatures low.<br />
<br />
<br />
=== Operation with input voltage variation of ±10%, full load ===<br />
The following set of measurements were obtained for input voltage variation while supplying full load current:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN</sub> Deviation'''</center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''I<sub>IN'''</sub></center><br />
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''V<sub>OUT'''</sub></center><br />
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''I<sub>OUT'''</sub></center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>+10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>51.86</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.41</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>–10%</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>42.52</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2.92</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>12.000</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>9.95</center><br />
<br />
|}<br />
'''Table 8.7: Input Voltage Variation, at Full Load'''<br />
<br />
<br />
No V<sub>OUT</sub> deviation was measured with variation of input voltage over ±10%.<br />
<br />
<br />
=== Thermal Infra-Red Imaging Of Full-Load Operation ===<br />
By calculation, at full-load, Regulator is dissipating 5.408W. Since Regulator has no forced-air or heatsink cooling, thermal infra-red imaging was performed. Length of time Regulator was ON before imaging was 2 minutes due to load allowable dissipation limitation. A future measurement should be taken after a long time (30 minutes) of operation with no airflow.<br />
<br />
<br />
Thermal IR photos were taken as shown below in <u>Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation</u>:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.4: Thermal IR Image, Full Load, 2 minutes of operation''']]<br />
<br />
<br />
For a 2 minute operation, the hottest component was D3 at about 75°C.<br />
<br />
<br />
Diode D3 was installed in parallel with MOSFET M2 as supplemental protection to provide a conducting path for inductor current during the dead time when both MOSFETs are off. This diode supplements the MOSFET body diode. However, M2 has an exposed pad soldered to PCB thermal vias. D3 is a SMD device situated above the PCB and it is not in thermal contact with the PCB. Such design protects MOSFET M2 from over-voltage damage, but results in a hot diode D3. Future PCB design may use a larger diode or one with better dissipation into device terminations (and therefore the PCB).<br />
<br />
<br />
Other major circuit components are prominent in thermal imaging. <br />
<br />
<br />
If waveforms show quick switching, may reduce dead time as well. Indicates insufficient device, slow M2, or excessive dead time. <br />
<br />
<br />
=== Output Voltage Ripple ===<br />
Measurement of Regulator output shows ripple and transients of various frequencies (<u>Figure 8.5: Regulator Output Voltage Ripple and Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.5: Regulator Output Voltage Ripple and Transients''']]<br />
<br />
<br />
Output voltage ripple is exceeding 500mV (<u>Figure 8.6: Output Voltage Ripple</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.6: Output Voltage Ripple''']]<br />
<br />
<br />
Periodic waveforms are observed with frequencies of 104kHz and 208kHz.<br />
<br />
<br />
In addition, there are transients (voltage spikes) present (<u>Figure 8.7: Output Voltage Transients</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.7: Output Voltage Transients''']]<br />
<br />
<br />
These transients consist of very fast ringing (<u>Figure 8.8: Output Ringing</u>) extending into the MHz range:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.8: Output Ringing''']]<br />
<br />
<br />
The magnitude and frequency of output transients and ringing, as well as magnitude of ripple, are unacceptable. TI Webench design does not use extensive output decoupling specified in controller IC datasheet, most likely to keep costs and size of the PCB down. Reduction of output ripple and transients will require addition of several output decoupling capacitors of different capacitances and materials, added in parallel, as it is standard industry practice. Current PCB does not allocate nearly enough space for the additional capacitors.<br />
<br />
<br />
See <u>9.5</u> <u>Output Capacitance</u> for improved test results.<br />
<br />
<br />
=== Gate Control Voltage for Both MOSFETs ===<br />
Oscilloscope measurement (<u>Figure 8.9: M2 Gate Control Voltage</u>) shows gate control voltage magnitude for M2 MOSFET is 7.2V. This is sufficient voltage to turn ON Logic Level Gate MOSFETs, but may be insufficient to turn ON “standard” control voltage MOSFETs. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.9: M2 Gate Control Voltage''']]<br />
<br />
<br />
Since MOSFET M1 is a NMOS, high-side switching is required as gate control voltage must exceed Regulator input voltage. This higher voltage is obtained inside the controller IC with a bootstrap voltage. <u>Figure 8.10: M1 Gate Control Voltage</u> shows a gate control voltage 56–48=8V higher than power supply. A fast switching waveform is seen, indicating that controller IC is able to supply enough current to charge and discharge MOSFET input capacitance quickly. However, a bootstrap supply cannot provide static (steady) voltage, which is evident by gate voltage droop. <br />
<br />
[[Image:|thumb|'''Figure 8.10: M1 Gate Control Voltage''']]<br />
<br />
<br />
A certain amount of dead time is required to avoid shoot-thru. <u>Figure 8.11: MOSFETs Dead Time</u> shows about 104ns of dead time. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.11: MOSFETs Dead Time''']]<br />
<br />
<br />
At full load, oscilloscope measurements were taken (<u>Figure 8.12: Full Load Duty Cycle - ON Time</u> and <u>Figure 8.13: Full Load Duty Cycle - Total Time</u>) to obtain Regulator duty cycle information.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.12: Full Load Duty Cycle - ON Time''']]<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.13: Full Load Duty Cycle - Total Time''']]<br />
<br />
<br />
Duty cycle percentage can now be found:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>D=\frac{\mathit{ON}\mathit{Time}}{\mathit{Total}\mathit{Time}}=\frac{2.44\mathrm{\mu }s}{9.56\mathrm{\mu }s}=0.255=25.5\text{\%}</math></center><br />
! <div align="right">(8.4)</div><br />
<br />
|-<br />
<br />
|}<br />
Regulator switching frequency can now be found<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>f=\frac{1}{\mathit{cycle}\mathit{time}}=\frac{1}{9.56\mathrm{\mu }s}=105\mathit{kHz}</math></center><br />
! <div align="right">(8.5)</div><br />
<br />
|-<br />
<br />
|}<br />
=== Turn-ON Settling Time (into full load) ===<br />
As shown below in <u>Figure 8.14: Power Supply Settling Time</u>, power supply takes about 12ms to reach 38 volts.<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.14: Power Supply Settling Time''']]<br />
<br />
<br />
Once UVLO is exceeded, Regulator takes about 1.2ms to settle to regulated output (<u>Figure 8.15: Voltage Regulator Output Settling Time</u>):<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.15: Voltage Regulator Output Settling Time''']]<br />
<br />
<br />
=== Minimum input voltage ===<br />
Regulator minimum voltage is limited by UVLO activation at 35V. Output voltage is ±0.01V from V<sub>IN</sub><nowiki>=48V down to UVLO level.</nowiki><br />
<br />
<br />
=== Inductor Voltage Waveform ===<br />
Inductor Voltage Waveform is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.16: Inductor Voltage Waveform''']]<br />
<br />
<br />
For a representative inductor current waveform, see <u>8.5.13</u> <u>Sense Resistor Current Waveform</u>. <br />
<br />
<br />
=== Transient Response Testing ===<br />
Testing to be performed:<br />
<br />
* Momentary upset capability (output voltage drop by <1V)<br />
* Input voltage transient capability<br />
<br />
Author has no capability at this time to perform Transient Response Testing. <br />
<br />
<br />
=== Sense Resistor Current Waveform ===<br />
Sense resistor current waveform is representative of inductor current waveform, as direct measurement of current in series with inductor may be difficult and / or affect circuit operation. <br />
<br />
<br />
[[Image:|thumb|'''Figure 8.17: Sense Resistor Current Waveform''']]<br />
<br />
<br />
Rsense was measured to be 5.422mΩ, but due to test lead limitations, measurements were made 5mm from each resistor lead. Assuming Rsense is 5mΩ as rated, ripple current thru inductor MEASUREMENT MAGNITUDE AND POLARITY MAKE NO SENSE.<br />
<br />
<br />
=== Current Overload / Short-Circuit Behavior ===<br />
To test current overload behavior, a load resistor of 499.1mΩ (excluding test leads resistance) was placed at output. V<sub>IN</sub> = 48V. A current output of 13.24 to 13.6 was obtained. <br />
<br />
<br />
Since this was below 15A limiting requirement, a “dead short” was created by connecting test leads together, without any series resistance. An output current of 25.8A was obtained, with an output voltage no longer compliant to 12V. This was more current than was expected. <br />
<br />
<br />
On investigation of datasheet [1] page 17 equation<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{I}_{\mathit{PEAK}\left(\mathit{LIMIT}\right)}=1.1-\frac{\frac{25\mathrm{\mu }\ast {t}_{\mathit{ON}}}{{C}_{\mathit{RAMP}}}}{{A}_{\mathit{SENSE}}x{R}_{\mathit{SENSE}}}=1.1-\frac{\frac{25\mathrm{\mu }\ast \left(0.25\ast \frac{1}{100k}\right)}{1.5n}}{10\ast 5m}=21.17A</math></center><br />
! <div align="right">(8.6)</div><br />
<br />
|-<br />
<br />
|}<br />
Since desired short current limit is 15A, re-design requires a 7mΩ, physically wider sense resistor (see <u>9.10</u> <u>Sense Resistor Re-Design</u>). <br />
<br />
<br />
=== Control Loop Voltage Waveform ===<br />
DC-coupled measurement of control loop voltage is shown below:<br />
<br />
<br />
[[Image:|thumb|'''Figure 8.18: Control Loop Voltage, DC-Coupled''']]<br />
<br />
<br />
Same, but AC-coupled to show detail is shown below:<br />
<br />
[[Image:|thumb|'''Figure 8.19: Control Loop Voltage, AC-Coupled''']]<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Design Improvements =<br />
TI Webench designs seems to be targeted for low cost. Parts specified are not adequate for the requirements, and are not in line with datasheet recommendations. Test data shows inadequate capabilities of the circuit. <br />
<br />
<br />
The following are the most obvious shortcomings of the design, and areas for improvement:<br />
<br />
<br />
Proj section: design improvements:<br />
<br />
Input caps in series to mitigate failure<br />
<br />
More input capacitance<br />
<br />
Feedback dc resistor<br />
<br />
Snubber<br />
<br />
Ceramics output caps in parallel. 25v rating<br />
<br />
Better diode<br />
<br />
Fuse<br />
<br />
Zero ohm resistor or similar as ic catastrophic short fuse<br />
<br />
<br />
BOM – schematic compare. Issues found see notebook<br />
<br />
<br />
document full schematic as marked up<br />
<br />
<br />
document schematic with PCB provisional parts / posts shown<br />
<br />
<br />
== IC Controller improvements ==<br />
The following is a list of improvements which can be made to the IC Controller and direct supporting circuitry:<br />
<br />
<br />
=== Power Supply ===<br />
IC requires an internal regulated voltage source of 7.4 volts. IC is capable of using an internal linear voltage regulator. However, linear voltage regulators are lossy, and as a rough estimate the IC will have to generate and dissipate up to an amount of power of:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center><math>{P}_{D\left(\mathit{LDO}\right)}=\left({V}_{O}-{V}_{\mathit{REG}}\right)\ast {I}_{\mathit{IC}}=\left(48-7.4\right)\ast 26m=1W</math></center><br />
! <div align="right">(9.1)</div><br />
<br />
|-<br />
<br />
|}<br />
Datasheet specifies a typical V<sub>CC</sub> Sourcing Current Limit of 26mA.<br />
<br />
<br />
IC is also capable of instead being powered off of its own output voltage of 12V (as long as datasheet parameters and guidelines are met). This will both improve efficiency and reduce amount of heat generated by the IC. <br />
<br />
<br />
A “jumper” wire was added from the VCCX post to VOUT.<br />
<br />
<br />
power IC controller off of output voltage (thru protection resistor and Zener?)<br />
<br />
<br />
Thermal image of 30-min operation after change.<br />
<br />
<br />
=== Voltage Rail Protection ===<br />
A pin of the IC controller is connected directly to the high-voltage, high-current voltage rail. If a short-circuit condition developed inside the IC, resulting current may be not large enough to melt the Input Protection Fuse, but may be enough to damage IC controller and / or nearby electronic components. A fuse in series with IC supply input should be used for a high-reliability design. Its current rating depends on the maximum current which can be carried by IC substrate and bond wires. An exact rating is not given, but a value of 100mA seems reasonable from datasheet interpretation. Fuse type should be fast blow. <br />
<br />
<br />
== Snubber ==<br />
According to [2, pg. 441], “Snubber circuits reduce power losses in a transistor during switching ... and protect the device from the switching stresses of high voltages and currents.” <br />
<br />
<br />
Output voltage shows ringing of 150MHz and an amplitude of 700mV (see <u>9.5</u> <u>Output Capacitance</u>). This is the highest magnitude of transients remaining at output, and this energy should be removed from output.<br />
<br />
<br />
Usual methods to prevent this energy from reaching switching device and circuit load is to use an absorbing snubber (series connection of capacitor and resistor) to common, in order to absorb and dissipate high-frequency transients in the resistor. This method requires an appropriately-sized (power) resistor, and will result in losses, as well as increase of PCB temperature.<br />
<br />
<br />
An “energy recovery snubber” may be used to re-circulate captured energy to circuit input instead of merely dissipating that energy as heat, but at the expense of greater circuit complexity and potential for erroneous design and circuit failure. This subject is beyond the scope of this report. <br />
<br />
<br />
FC=1MHz. Snubber critical frequency / application note?<br />
<br />
Estimate energy in HF transient from scope screenshot.<br />
<br />
<br />
== Free-Wheeling Diode ==<br />
This diode supplements synchronous rectification MOSFET during dead time(s) (see <u>8.5.8</u> <u>Gate Control Voltage for Both MOSFETs</u>) twice during each switch period. MOSFET body diode has V<sub>F</sub><nowiki>=500mV, while a Schottky diode type has V</nowiki><sub>F</sub><nowiki>=300mV</nowiki>. A purpose-built diode for this application can be more ruggedized (avalanche rating, switching speed, etc). <br />
<br />
<br />
Diode should have the following characteristics:<br />
<br />
* Schottky type.<br />
* I<sub>F</sub> needs to be equal to I<sub>L(MAX)</sub> or higher.<br />
* PD rating needs to factor in temperature rise due to amount of current passed thru the diode during two times of conduction in each switch cycle, and Θ. <br />
<br />
== Input capacitance ==<br />
Current shorts (“short circuit”) internal to an input capacitor which is placed between a high-voltage, high-current input voltage and common pose a risk of damage to the PCB, nearby electronic components, and solar panel powering the Regulator. An input protection fuse (<u>7.2.6</u> <u>Input Protection Fuse</u>) has been implemented to disconnect the Regulator from the Solar Panel Array if a short circuit develops inside an input capacitor. <br />
<br />
<br />
One risk mitigation strategy is to connect two capacitors in series. This halves the risk, but has the following drawbacks:<br />
<br />
<br />
* ESR of capacitor string is doubled.<br />
* Voltage rating of each capacitor must remain same as if one capacitor was used (e.g. half the voltage rating should not be used), since should a single capacitor short-circuit, the remaining one will experience full voltage potential across the remaining device. In addition, voltage balancing resistors of high resistance may be used to divide voltage between capacitors equally.<br />
* Capacitance of capacitor string is halved compared to capacitance of the individual capacitors.<br />
* In order to have a collection of capacitors equal to an individual one in terms of capacitance, ESR, and voltage rating, ''four'' capacitors need to be placed in a series-parallel configuration (see <u>Figure 9.1: Capacitors Series-Parallel Connection</u>). <br />
<br />
[[Image:|thumb|'''Figure 9.1: Capacitors Series-Parallel Connection''']]<br />
<br />
<br />
An additional reason for voltage-balancing resistor is that certain capacitor materials show a decrease in capacitance proportional to magnitude of applied voltage across the capacitor. This de-rating of capacitance can be significant for some dielectric materials. <br />
<br />
<br />
Amount of capacitance from datasheet. Input aluminum capacitor. <br />
<br />
<br />
== Output Capacitance ==<br />
Webench chose capacitor voltage rating of 16V for an output voltage of 12V. A good design margin is a capacitor voltage rating of 1.5 times the maximum node voltage. Nearest standard ratings are 20V and 25V. <br />
<br />
<br />
A common design strategy is to place several capacitors in parallel for reduction in overall ESR. As test results show an unacceptably large output ripple (see <u>8.5.7</u> <u>Output Voltage Ripple</u>), much larger capacitance and much lower ESR is required at the output of the Regulator. <br />
<br />
<br />
Test results also show transients with frequencies of 104kHz, 208kHz, and 150MHz. Several types of capacitor materials are needed to filter out the different frequency ranges. Ceramic capacitors are better suited for higher frequencies. <br />
<br />
<br />
Amount of capacitance<br />
<br />
Resistor in series with electrolytic to prevent it from absorbing high-frequency energy and damage to capacitor???<br />
<br />
<br />
As an investigation, four 3.3μF, 25V ceramic (part number? material?) capacitors were added in parallel at the output (Figure 9.2: COUT Ceramic Capacitors in Parallel).<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.2: COUT Ceramic Capacitors in Parallel''']]<br />
<br />
<br />
Output voltage has improved significantly. Below is measurement of highest magnitudes (1.1V) of observable transients:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.3: VOUT Transients, Four Additional Ceramic Capacitors''']]<br />
<br />
<br />
Output voltage ripple has also improved significantly, down to 150mV:<br />
<br />
<br />
[[Image:|thumb|'''Figure 9.4: VOUT Ripple, Four Additional Ceramic Capacitors''']] <br />
<br />
<br />
High-frequency ringing has decreased in magnitude:<br />
<br />
<br />
[[Image:]] <br />
<br />
<br />
However, an absorbing or recirculating snubber (see <u>9.2</u> <u>Snubber</u>) should be added to the output to remove this ringing.<br />
<br />
<br />
Peak capacitor current is ΔiL/2 = 1.44 A, and rms capacitor current for the triangular waveform 1.44/ sqrt(3) = 0.83 A.<br />
<br />
<br />
== MOSFET, Active Switch ==<br />
A new choice for a MOSFET would need to satisfy the following criteria:<br />
<br />
* Device must have a rating of V<sub>DSmax</sub> ≥ 60V due to the input voltage maximum specification of 52V. A 80-100V device is recommended. <br />
* V<sub>GS(ON)</sub>: based on empirical data, IC controller supplies a control V<sub>GS</sub> of ~7V. MOSFET should be ON fully at this gate voltage. MOSFET will cause power loss due to R<sub>DS(ON)</sub> presented by the transistor at this gate voltage. <br />
* R<sub>DS(ON)</sub> should be as little as possible, without excessive input capacitance typical of massively parallel devices. <br />
* Gate charge (capacitance). Total gate charge is limited by the current that the IC controller output drivers can supply at the necessary transition speed. In addition, power lost driving MOSFET gates will subtract from circuit efficiency and cause higher IC temperature. <br />
* I<sub>D</sub>: needs to be rated for at least the I<sub>L(RMS)</sub>. Recommend device to be rated for I<sub>L(MAX)</sub>. See section <u>7.2.5</u> <u>Inductor</u>.<br />
* P<sub>D</sub> is determined by losses of the MOSFET. Factors contributing to loss are: R<sub>DS(ON)</sub> static dissipation when device is fully ON at the driven gate voltage, losses due to MOSFET not being fully ON during switching transitions, and energy needed to drive gate total charge. <br />
<br />
Oscillator = MOSFET switching time X 100<br />
<br />
MOSFET switching speed should be 1/10 of T<sub>ON</sub>. Gate drive current. <br />
<br />
<br />
== MOSET, Synchronous Rectification ==<br />
Criteria for synchronous rectification MOSFET is same as for <u>9.6</u> <u>MOSFET, Active Switch</u>, with the following differences:<br />
<br />
<br />
* I<sub>D(RMS)</sub> = I<sub>L(RMS)</sub>, but recommended device I<sub>D</sub> should be equal or exceeding I<sub>L(MAX)</sub>. <br />
* P<sub>D</sub>: MOSFET is ON for the amount of time ''less'' the adaptive dead time (see IC controller datasheet). During the dead time, parallel free-wheeling diode D3 conducts instead due to its lower Schottky V<sub>F</sub> of ~0.3V.<br />
<br />
free-wheeling diode V<sub>F</sub> at rated current?<br />
<br />
<br />
== MOSFET Gate Protection Resistors ==<br />
MOSFET Gate Protection Resistors may be used in circuit to serve four functions:<br />
<br />
* They will limit current drawn by MOSFET gate from IC controller during fast charge / discharge of the gate capacitor. Note that excessive slowing down of MOSFET switch speed will result in power loss to internal dissipation, and increase likelihood of shoot-thru. <br />
* In the event of MOSFET gate dielectric punch-thru failure, they will limit current entering IC controller output from the shorted Drain-Source channel. Note that the controller already has a low-value built-in resistance at its outputs. <br />
* They will limit current flowing from IC controller output to provisional MOSFET Gate Protection Zeners (see <u>9.9</u> <u>MOSFET Gate Protection Zeners</u>).<br />
* They can be used as current shunts for oscilloscope voltage measurements of dynamic current supplied from IC controller into MOSFET gate terminal. <br />
<br />
== MOSFET Gate Protection Zeners ==<br />
This is a provisional protection device. Its necessity will be evaluated after the test phase of this project. <br />
<br />
<br />
== Sense Resistor Re-Design ==<br />
Sense resistor chosen by Webench is not fitting its land (see Figure 9.5: Rsense Too Small For Its Land), and a larger component is required for re-design. <br />
<br />
<br />
[[Image:|thumb|'''Figure 9.5: Rsense Too Small For Its Land''']]<br />
<br />
<br />
In addition, Webench has suggested a wrong current limit value (see 8.5.14 Current Overload / Short-Circuit Behavior). For project specification of 15A current limit, a 7mΩ resistor is required. <br />
<br />
<br />
== Inductor Re-Design ==<br />
Three findings are cause for inductor re-design:<br />
<br />
<br />
# Webench uses a guideline of I<sub>L(max)</sub> = 0.4 * I<sub>O</sub><br />
# Currently specified inductor enters a -10% decrease of inductance at circuit I<sub>L(max)</sub> of 12.05A (see <u>Table 7.1: Inductor, Webench</u>)<br />
# Large current ripple will require a larger output capacitor (or capacitors bank), and more importantly will result in shorter capacitor life span. <br />
<br />
For three reasons above, re-design will use an inductor with the following specifications:<br />
<br />
<br />
L core loss at 100kHz?<br />
<br />
<br />
= Conclusion =<br />
On a very short timetable and a small budget, a DC-DC regulator was designed, sourced, assembled, and tested. Instances where theoretical predictions differed from practical measurements required minor circuit re-design.<br />
<br />
<br />
Once Digi-Key selection tool has narrowed down controller IC choices, Texas Instruments Webench was very useful for initial circuit design, and has saved designer from laborious calculations and design choices. <br />
<br />
<br />
Circuit total BOM was within available budget.<br />
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<br />
Circuit assembly was mostly straightforward, although there are some errors with Webench BOM.<br />
<br />
<br />
PCB testing was mostly successful, with some exceptions of performance from Webench claims.<br />
<br />
<br />
Circuit failed performance specifications for input and output ripple voltage, due to inadequate filtering capacitance. The practical aspect of capacitor ESR was cause of difference from theory to practice. <br />
<br />
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Output current limiting threshold, and physical size of current sense resistor was the other major design flaw. <br />
<br />
<br />
With exception of issues outlined above, this designed and assembled DC-DC regulator performs in converting 48V±10% into a 12V, 10A output, with an ≈95% efficiency.<br />
<br />
<br />
Circuit sourcing, construction, and testing has revealed important practical and real-life electronics concepts and behaviors. Difference from simplified theoretical discussion to practical design aspects is the experience gained as a result of real-life construction and testing.<br />
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<br />
<br />
<br />
<br />
<br />
= References =<br />
[1] LM5116 Wide Range Synchronous Buck Controller. Datasheet. Texas Instruments. Revision G.<br />
<br />
<br />
[2] D. W. Hart, “Power Electronics”. McGraw-Hill, 2011<br />
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<br />
<br />
<br />
<br />
<br />
= Appendix A – Bill of Materials =<br />
<u>Table 12.1: BOM at Beginning of Project</u> shows expenditures at beginning of this project:<br />
<br />
<br />
[[Image:|thumb|'''Table 12.1: BOM at Beginning of Project''']]<br />
<br />
<br />
Total developmental cost<br />
<br />
Add COUT ceramic caps<br />
<br />
Correct BOM errors<br />
<br />
<br />
<br />
<br />
<br />
<br />
= Appendix B – Labor =<br />
Labor required by this project is documented below in <u>Table 13.1: Project Labor</u>:<br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Labor Type</center><br />
! <center>Amount, in Hours</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Initial design and sourcing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>16</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>PCB assembly</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>8</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Test setup and harness build</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Full-load testing</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>4</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Documentation total to date</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>30</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Total:'''</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>'''48'''</center><br />
<br />
|}<br />
'''Table 13.1: Project Labor'''<br />
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<br />
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<br />
<br />
= Appendix D – List of Printed Attachments =<br />
The major circuit components will have printed datasheets attached at the end of this report. <br />
<br />
<br />
<br />
{| style="border-spacing:0;"<br />
! <center>Number</center><br />
! <center>Title</center><br />
! <center>Category</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>1</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Switch</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>2</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>MOSFET, Rectifier</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
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|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>3</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Inductor</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
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|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>4</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Output Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Capacitor, Input Filtering</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>5</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>LM5116 Wide Range Synchronous Buck Controller</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|-<br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>6</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>Diode, free-wheeling</center><br />
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| <center>Datasheet</center><br />
<br />
|}<br />
D1 is not on BOM!<br />
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[Slide] Load regulation specifies how much change occurs in the output voltage for a given range of load current values, usually from no load (NL) to full load (FL).<br />
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Remarks from all datasheets<br />
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Proj device average, peak ratings. Q C D L. Pd<br />
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why highly necessary data not included in capacitor datasheet: Because it is critically value-specific. Use manufacturer's calculator tool. Or look up deviation by dielectric material type. <br />
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wtf schematic is all fucked up in size: seemingly huge size, but tiny font???<br />
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resistor in series with COUT electrolytic<br />
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<br />
Digitize binder notes<br />
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2M resistor across Ccomp2 to stabilize (reduce from 80dB) DC gain<br />
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1ohm resistor in series with Cout electrolytic. HF ripple prevented from destroying capacitor, and short current. same for cin electrolytic. will limit inrush current on low impedance dc power supply connection. <br />
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3-4uF ceramic capacitors in parallel at output (done)<br />
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TIMA simulation would have SPICE models for TI components<br />
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Need {capacitance, ESR} in relation to {voltage, frequency, ripple current, temperature}<br />
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D2, at 2A, is entirely inappropriate for the design. Need a diode with rating of Vmax=Vsupply, Amax=Ashort+Aripple???<br />
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app note for power MOSFETs<br />
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snubber app note<br />
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snubber reduces the power loss in the transistor<br />
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reduce voltage and current stresses in the transistor<br />
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Snubber provisional diode across top resistor<br />
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<br />
SPICE sim with HS drive and synchronous rectification.<br />
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Open Mode capacitors for input<br />
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<br />
Wikipedia article on ceramic capacitors<br />
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<br />
approximate “heatsink” thermal resistance based on PCB area<br />
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<br />
FET gate drive magnitude with VCCX<br />
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Transients, transient energy, and FFT at switch node<br />
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Snubber must protect bottom MOSFET. Snubber and output filtering must protect vccx<br />
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<br />
Open Mode capacitors. for input (exposed to outside voltages) capacitors<br />
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Syfer 2220Y0630335KXT<br />
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flexible termination.<br />
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no sizes above 1210 due to bending issues, unless they are flex term.<br />
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why Steve wants to eliminate all thru-hole parts from our products???<br />
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<br />
an aluminum thru-hole input cap would relieve tension, and is not brittle like a ceramic.<br />
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Remove RS power res from BOM, cost estimate<br />
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Frequency and energy of transients<br />
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re-do thermal photo with VCCX<br />
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Dead time must be longer than reverse recovery time of sync fet<br />
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Is my gate drive now 12v<br />
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Open mode or flex term caps perpendicular to ea<br />
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New dmm cal info<br />
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Equipment serial numbers<br />
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re-design summary:<br />
<br />
* cin aluminum<br />
* cout ceramic<br />
* snubber C R D<br />
* properly sized freewheeling diode<br />
* rsense<br />
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Further improvement to report, only for my own benefit:<br />
<br />
* energy recovery snubber for buck converter<br />
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<math>{\mathrm{\Theta }}_{\mathit{thermal}}=\frac{{T}_{\mathit{destination}}-{T}_{\mathit{source}}}{{P}_{D}}</math><br />
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<br />
<math>{T}_{\mathit{junction}}={P}_{D}\ast \left({\mathrm{\Theta }}_{\mathit{total}}\right)+{T}_{\mathit{ambient}}</math><br />
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<br />
<br />
----<br />
<references/></div>
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