dm00025079

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
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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
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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
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