AN3373 Application note IEEE802.3at compliant PD + PS design based on PM8803 low power, synchronous flyback PoE converter Introduction PM8803 is a highly integrated device embedding an IEEE802.3at compliant powered device (PD) interface together with a PWM controller and support for auxiliary sources. Figure 1 is an image of the PM8803 demonstration board. The same PCB can be populated with different components to support various configurations and topologies: synchronous flyback with or without active clamp, flyback with diode rectification, synchronous forward with or without active clamp, forward with diode rectification. This document focuses on a reference design for a high efficiency, low power PD (up to 7 W) power converter based on flyback topology with synchronous rectification using the PM8803 as the main controller. This converter can be derived from a PM8803 demonstration board with a few component changes. Schematics of the PoE converter are given in Section 2 while the related bill of material is detailed in Section 3. In Section 4 efficiency measurements, together with the main waveforms of the PoE interface and the flyback converter, are shown. Figure 1. April 2011 PM8803 FLY demonstration kit Doc ID 018626 Rev 1 1/18 www.st.com Contents AN3373 Contents 1 Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Demonstration kit schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4 Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1 Efficiency measurements with synchronous rectification . . . . . . . . . . . . . 10 4.2 Converter waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2.1 Startup sequence from PoE injectors . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2.2 Primary side MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2.3 Secondary side MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2.4 Load transient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.2.5 Output ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Appendix A Efficiency measurements with diode rectification . . . . . . . . . . . . . 16 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2/18 Doc ID 018626 Rev 1 AN3373 1 Electrical specifications Electrical specifications Table 1. Specifications for 3.3 V output Parameter Description Min. Input voltage range Applied at J3 connector 0 57 V 42 57 V 36 V Operative input voltage Typ. Max. Vin rising edge Unit UVLO Vin falling edge Auxiliary input voltage range 30 V 35 Output voltage (Vout) Vin = 42 V to 57 V, Iout 0 to Imax 3.25 Output current (Iout) Vin = 42 V to 57 V 0 Peak-to-peak output ripple 48 Vin, Iout = Imax 3.35 50 60 V 3.45 V 2 A 70 mVpp Inrush current limit 140 mA DC current limit 440 mA Efficiency DC-DC only Vin = 48 V, Iout = Imax 90 % Overall efficiency Vin = 48 V, Iout = Imax 88 % 250 kHz Switching frequency Doc ID 018626 Rev 1 3/18 &KDVVLV $8; '$7$32:(5,1387 - 63 - )HUULWH%HDGRKP$ 10 & ' 60$ ' 63 60$ 6736+$ ' 60$ 6736+$ 677+5$ &KDVVLV & Q) .9 & Q) 9 60$ ' ' ')610 60$ 6736+$ ' 6736+$ & Q) 9 5 5 5 5 . 5 )HUULWH%HDGRKP$ & Q) 9 & Q) 9 5 5 $X[LOLDU\LQSXWIURQWDORU$8; 5 5 5 5 60$ 6736+$ ' 60$ 6736+$ ' 60$ 6736+$ ' ' ')610 60$ 6736+$ ' (7+/' 7 (7+/' 7 & Q) 9 5 )HUULWH%HDGRKP$ & Q) 9 966 & 10 9 32() & Q) 9 ,QSXW&RPPRQ0RGH)LOWHU )HUULWH%HDGRKP$ 5 :XUWK6 710 Doc ID 018626 Rev 1 9 & Q) 60$ & Q) 9 60$-$ ' & Q) 9 966 571 32() &KDVVLV & Q) 9 & X) 9 5 10 & Q) 9 9287 &KDVVLV &KDVVLV - '$7$287387 Figure 2. 4/18 2 &KDVVLV Demonstration kit schematic AN3373 Demonstration kit schematic Demonstration kit schematic: detail of the input section including data transformers, diode bridges, protection, and optional CM choke !-V Doc ID 018626 Rev 1 & Q) 5 . 5 . 6$ - 5 5 & 10 5 . 5 N 5 5 & 10 9'' 9'' '(7 63 &/6 '&&/ 6$ '7 )56 73 8 ([3DG ' 5 5 & X) 9 571 ,QSXW)LOWHU 571 62' 5 5 X) 9 & %$7- ' X) 9 & ' 5 5 5 & 10 Q) 127(IRU&DSDFLWRUV :KHUHQRWLQGLFDWHGWKHERG\LVDQGWKHYROWDJHLV9 $571 & S) 3RZHUFLUFXLW 10 5 5 . 5 X+ 62' & X) 9 . $571 & X) 9 & X) 9 [ / %$7- 5 . 5 5 & X) 9 0660/ 9 & 966 571 $571 *$7 9& *$7 571 &6 9% &7/ 30FLUFXLW +76623 30 5 . Q) & 5 . 60& 677+5$ 571 127(IRU5HVLVWRUV :KHUHQRWLQGLFDWHGWKHERG\LVDQGWROHUDQFH 10 & 5 . 5 )HUULWH%HDGRKP$ 5 . 5 )HUULWH%HDGRKP$ 966 63 32() 9$8; 4 5 RKP 6RW 6761) 10 7 .9 571 Q) & Q) & 5 . 5 5 Q) ' & ' %$762' %$762' 6\QFKURQRXVPVRIHWGULYHU 7 &2,/&5$)7'$$/ &2,/&5$)732(3/ & 5 & 10 571 & Q) 5 . $571 4 00%7/7 627 5 5 62 6761/+ 4 5 8 ' & .9 Q 62' & X) 9 %$7- & & & Q) 5 . S) 5 & X) 9 Q) & X) 9 [ )HHGEDFNFLUFXLW 627 8 62' %$7- ' 5 5 X) 9 & 76$,/7 5 . & Q) X) 9 X) 9 )DLUFKLOG)2'$6 & & 5 N 5 N 5 5 - Figure 3. AN3373 Demonstration kit schematic Demonstration kit schematic: detail of the PoE converter based on flyback topology with synchronous rectification !-V 5/18 Bill of material Bill of material 6/18 3 Table 2 shows the bill of material for the PoE converter based on the PM8803. Table 2. Bill of material Doc ID 018626 Rev 1 Qty. Reference Description Value Tol. Body Vendor 1 EVALPM8803 FLY rev1 Board PCB 8 C1,C2,C3,C4,C11C36,C44,C45 Ceramic capacitor 100 nF 50 V 603 Std 4 C5,C6,C7,C8 Ceramic capacitor 10 nF 10% 100 V 603 TDK 6 C10,C39,C41,C48C53,C59 Ceramic capacitor 1 µF 20% 16 V 603 Std 1 C12 Ceramic capacitor 2.2 nF 2 kV 1812 TDK 3 C14,C16,C21 Ceramic capacitor 1 nF 100 V 603 TDK NM C15,C24,C30 Ceramic capacitor NM 805 NM 2 C19,C38 Ceramic capacitor 22 nF 603 Std NM C22 Ceramic capacitor NM 1812 NM 1 C26 Aluminium capacitor 22 µF 20% 100 V 810x10.2 Std Low ESR 3 C27,C33,C37 Ceramic capacitor 22 µF 20% 6.3 V 805 Std 2 C28,C29 Ceramic capacitor 1 µF 20% 100 V 1206 TDK 1 C31 Ceramic capacitor 1 nF 10% 100 V 805 Std 2 C32,C60 Ceramic capacitor 0.1 µF 10% 100 V 805 TDK 1 C34 Aluminium capacitor 330 µF 6.3 V 8x10.2 Std Low ESR NM C40 Ceramic capacitor NM 805 NM NM C43 Aluminium capacitor NM 4x6 NM NM C47,C66,C69 Ceramic capacitor NM 603 NM 1 C49 Ceramic capacitor 10 nF 50 V 603 Std 1 C50 Ceramic capacitor 100 nF 50 V 603 Std 1 C54 Ceramic capacitor 470 pF 50 V 603 Std 10% 50 V AN3373 Voltage Bill of material (continued) Qty. Reference Description Value 1 C55 Ceramic capacitor 1 C56 1 Tol. Doc ID 018626 Rev 1 Voltage Body Vendor 100 pF 50 V 603 Std Ceramic capacitor 22 nF 50 V 603 Std C61 Ceramic capacitor 2.2 nF 2 kV 1812 TDK 1 D1,D21 Std diode STTH1R02A 200 V SMC ST 1 D32 Zener diode BZX84C10 SOT23 Std 8 D4,D7,D8,D9,D12D13,D14, D17 Schottky diode STPS1H100A SMA ST 1 D11 TVS diode SMAJ58A SMA ST 1 D23 Schottky diode STPS1H100A SMA ST NM D24,D25 Bridge rectifier NM SDIP NM 6 D28,D34,D36,D37D39,D40 Schottky diode BAT46J SOD323 ST 2 J1,J2 Power jack SA,SP Std 1 J3 RJ45 connector Data & power input Std 1 J4 RJ45 connector Data output Std 1 J5 Terminal block 2-way MOR-10X10.5-P5-2PIN Std 1 L5 SMT inductor 10 µH 1 Q12 Mosfet N-channel STS10N3LH5 1 Q16 Transistor, PNP 1 Q17 4 100 V 100 V 100 V Coilcraft 30 V SO8 ST MMBT3906LT1 40 V SOT23 Std Mosfet N-channel STS1NF20 200 V SOT223 ST R10,R11,R12,R13 Chip resistor 75 Ω 603 Std 6 R17,R26,R37,R43 R49,R54 Ferrite bead MPZ012101A 805 TDK NM R18 Chip resistor NM 1206 NM 2 R27,R58 Chip resistor 124 kΩ 603 Std 2 R32,R51 Chip resistor 100 kΩ 805 Std 100R,4A 1% 7/18 Bill of material MSS7341-103ML AN3373 Table 2. Bill of material (continued) Qty. Reference Description Value Tol. 4 R38,R65,R89, R104 Chip resistor 4.75 kΩ 1% 1 R53 Chip resistor 3 R60,R64,R68 1 Doc ID 018626 Rev 1 Vendor 603 Std 4R7 1206 Std Chip resistor 0Ω 603 Std R62 Chip resistor 68 Ω 603 Std 1 R70 Chip resistor 9.1 kΩ 1% 603 Std 1 R72 Chip resistor 91 kΩ 1% 603 Std 1 R80 Chip resistor 47 Ω 603 Std 2 R83,R107 Chip resistor 100 kΩ 603 Std 1 R89 Chip resistor 2.7 kΩ 603 Std 1 R90 Chip resistor 3.31 kΩ 603 Std 1 R91 Chip resistor 10 Ω 603 Std 1 R92 Chip resistor 150 Ω 603 Std 1 R93 Chip resistor 680 Ω 603 Std 1 R94 Chip resistor 21 kΩ 1% 603 Std 1 R95 Chip resistor 24.9 kΩ 1% 603 Std 1 R96 Chip resistor 0Ω 603 Std 2 R99,R101 Chip resistor 51 kΩ 1% 603 Std 1 R102 Chip resistor 80R6 1% 805 Std 1 R103 Chip resistor 510 Ω 603 Std 1 R104 Chip resistor 3.31 kΩ 1% 603 Std 1 R109 Chip resistor 0.47 Ω 1% 1206 Std low value 1 R111 Chip resistor 12.4 kΩ 1% 603 Std NM R125 Chip resistor NM 603 NM 2 T1,T2 POE+ Magnetics ETH1-230LD Coilcraft AN3373 Body 1% Voltage Bill of material 8/18 Table 2. Bill of material (continued) Qty. Reference Description Value Tol. Voltage Body Vendor NM T3 CM choke NM NM 1 T7 Power transformer POE13P-33L Coilcraft 1 T8 Gate driver transformer DA2319-AL Coilcraft 1 U1 POE+ controller PM8803 HTSSOP20 ST 1 U3 SMT optocoupler Fairchild FOD817AS 4PDIP Fairchild 1 U4 Shunt regulator TS431AILT SOT23-5 ST AN3373 Table 2. Doc ID 018626 Rev 1 Bill of material 9/18 Test results AN3373 4 Test results 4.1 Efficiency measurements with synchronous rectification Figure 4. Efficiency measurements at 48 V input 9(IILFLHQF\ORZSRZHUYV,RXW (IILFLHQF\ RYHUDOO9NK] GFGF9NK] RYHUDOO9$X[,,NK] ,RXW$ !-V Figure 5. Converter efficiency vs. input power 9(IILFLHQF\ORZSRZHUYV3LQ (IILFLHQF\ RYHUDOO9NK] GFGF9NK] RYHUDOO9$X[,,NK] 3LQ: !-V The difference between DC-DC and overall measurements is about 2% from 0.8 A to 2 A. 10/18 Doc ID 018626 Rev 1 AN3373 Test results 4.2 Converter waveforms 4.2.1 Startup sequence from PoE injectors Figure 6. Startup from an IEEE 802.3af injector with 2 A load !-V 4.2.2 Primary side MOSFET Figure 7. Primary side power MOSFET waveforms at 0 A load !-V Doc ID 018626 Rev 1 11/18 Test results AN3373 Figure 8. Primary side power MOSFET waveforms at 2 A load !-V 4.2.3 Secondary side MOSFET Figure 9. Secondary side power MOSFET waveforms at 0 A load !-V 12/18 Doc ID 018626 Rev 1 AN3373 Test results Figure 10. Secondary side power MOSFET waveforms at 2 A load !-V Figure 11. Detail of secondary side power MOSFET waveforms at 2 A load !-V Doc ID 018626 Rev 1 13/18 Test results 4.2.4 AN3373 Load transient Figure 12. Response of the converter to a 1 A - 2 A load transient !-V Figure 13. Response of the converter to a 0 A - 2 A load transient !-V 14/18 Doc ID 018626 Rev 1 AN3373 4.2.5 Test results Output ripple Figure 14. Output ripple measurement at 2 A !-V Figure 15. Output ripple measurement at 2 A with infinite persistence !-V Doc ID 018626 Rev 1 15/18 Efficiency measurements with diode rectification Appendix A AN3373 Efficiency measurements with diode rectification Figure 16. Efficiency measurements at 48 V input 9(IILFLHQF\ORZSRZHUYV,RXW (IILFLHQF\ RYHUDOONK] GFGFNK] RYHUDOOZLWKGLRGH$NK] GFGFZLWKGLRGH$NK] ,RXW$ !-V Figure 17. Delta efficiency comparison 'HOWD(IILFLHQF\YV,RXW 'HOWD(IILFLHQF\ 'HOWDHIILFLHQF\ZLWKGLRGH 'HOWDHIILFLHQF\ZLWK026)(7 'HOWDGLRGHZUW026)(7 '&'& 'HOWDGLRGHZUW026)(7RYHUDOO ,RXW>$@ !-V The difference between DC-DC and overall measurements is similar in both MOSFET and diode rectification, about 2% from 0.8 A to 2 A. The difference between MOSFET and diode rectification is similar in both DC-DC and overall measurements, about 6.5% from 0.8 A to 2 A. 16/18 Doc ID 018626 Rev 1 AN3373 Revision history Revision history Table 3. Document revision history Date Revision 06-Apr-2011 1 Changes Initial release Doc ID 018626 Rev 1 17/18 AN3373 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no liability whatsoever relating to the choice, selection or use of the ST products and services described herein. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. 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