UM1062
User manual
EVALPM8803-FWD: IEEE802.3at compliant demonstration kit
with synchronous active clamp forward converter
Introduction
The PM8803 is a highly integrated device embedding an IEEE802.3at-2009 compliant
powered device (PD) interface together with a PWM controller and support for auxiliary
sources.
Figure 1
is an image of the EVALPM8803-FWD PoE+ demonstration board. The
same PCB can be populated with different components to support various configurations
and options (active clamp forward both with synchronous rectification or with diode
rectification).
This document focuses on a reference design for PoE+ based on AC forward topology with
synchronous rectification, with the PM8803 as the main controller.
The schematics and board layout of the PoE+ section are given in
Section 2
and
3
while the
related bill of material is detailed in
Section 5.
In
Section 7
efficiency measurements
together with main waveforms of the PoE interface and AC forward converter are shown.
Figure 1.
EVALPM8803-FWD demonstration kit
March 2011
Doc ID 018571 Rev 1
1/31
www.st.com
Contents
UM1062
Contents
1
2
3
4
5
6
7
Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Demonstration kit schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
I/O connectors and test points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Power-up sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.1
7.2
7.3
Efficiency measurement with 3.3 V output . . . . . . . . . . . . . . . . . . . . . . . . 20
Efficiency measurement with 5 V output . . . . . . . . . . . . . . . . . . . . . . . . . 21
Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
7.3.1
7.3.2
7.3.3
7.3.4
7.3.5
7.3.6
7.3.7
Startup sequence from PoE/PoE+ injectors . . . . . . . . . . . . . . . . . . . . . . 23
Transition from PoE to auxiliary and auxiliary to PoE . . . . . . . . . . . . . . 24
Primary side MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Secondary side MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Line transient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Load transient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Output ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
8
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
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UM1062
List of tables
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Specifications for 3.3 V output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Specifications for 5 V output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Test points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
EVALPM8803-FWD BOM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
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List of figures
UM1062
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
EVALPM8803-FWD demonstration kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Demonstration kit schematic: detail of the PoE+ input section including data transformer,
diode bridges, protection, and optional CM choke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Demonstration kit schematic: detail of the PoE+ section based on AC forward topology
with synchronous rectification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Assembly view: top layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Assembly view: bottom layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Top layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Inner layer 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Inner layer 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Bottom layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Efficiency measurements at 48 V input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
DC-DC only efficiency measurements at different input voltages. . . . . . . . . . . . . . . . . . . . 20
Overall efficiency measurements at different input voltages. . . . . . . . . . . . . . . . . . . . . . . . 21
Efficiency measurements at 48 V input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
DC-DC only efficiency measurements at different input voltages. . . . . . . . . . . . . . . . . . . . 22
Overall efficiency measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Startup from an IEEE 802.3af injector with 2 A load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Startup from an IEEE 802.3at injector with 4 A load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Switching between PoE and auxiliary source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Primary side power MOSFET waveforms at 0 A load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Primary side power MOSFET waveforms at 4 A load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Secondary side power MOSFET waveforms at 0 A load . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Secondary side power MOSFET waveforms at 4 A load . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Effect of a 12 V line transient on the converter at 4 A load. . . . . . . . . . . . . . . . . . . . . . . . . 27
Effect of a 12 V line transient on the converter at 0 A load. . . . . . . . . . . . . . . . . . . . . . . . . 27
Response of the converter to a 2 A - 4 A load transient . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Response of the converter to a 0 A - 4 A load transient . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5 V output ripple measurement at 4 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5 V output ripple measurement at 4 A with infinite persistence . . . . . . . . . . . . . . . . . . . . . 29
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UM1062
Electrical specifications
1
Electrical specifications
Table 1.
Specifications for 3.3 V output
Parameter
Input voltage range
Operative input voltage
Vin rising edge
UVLO
Vin falling edge
Auxiliary input voltage range
Output voltage (Vout)
Output current (Iout)
Peak-to-peak output ripple
Inrush current limit
DC current limit
3.3 V efficiency DC-DC only
3.3 V overall efficiency
Switching frequency
Vin=48 V, Iout=Imax
Vin=48 V, Iout=Imax
Vin= 42 V to 57 V, Iout 0 to Imax
Vin= 42 V to 57 V
48 Vin, Iout=Imax
30
35
3.25
0
30
140
640
92
89
200
3.35
60
3.45
6
40
V
V
V
A
mVpp
mA
mA
%
%
kHz
Description
Applied at J3 connector
Min.
0
42
Typ.
Max.
57
57
36
Unit
V
V
V
Table 2.
Specifications for 5 V output
Parameter
Description
Applied at J3 connector
Min.
0
42
Vin rising edge
UVLO
Vin falling edge
30
35
Vin= 42 V to 57 V, Iout 0 to Imax
Vin= 42 V to 57 V
48Vin, Iout=Imax
4.95
0
30
140
640
Vin=48 V, Iout=Imax
Vin=48 V, Iout=Imax
92
89
200
5.1
60
5.25
4
40
V
V
V
A
mVpp
mA
mA
%
%
kHz
Typ.
Max.
57
57
36
Unit
V
V
V
Input voltage range
Operative input voltage
Auxiliary input voltage range
Output voltage (Vout)
Output current (Iout)
Peak-to-peak output ripple
Inrush current limit
DC current limit
5 V efficiency DC-DC only
5 V overall efficiency
Switching frequency
Doc ID 018571 Rev 1
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