AN2783
Application note
PM8800 demonstration kit for standard and high power PoE
PD interface and power supply, with auxiliary sources
Introduction
This document details the characteristics and performances of the PM8800 demonstration
kit which has been designed to cover a broad range of power over Ethernet (PoE)
applications. PM8800 is a highly integrated device embedding an IEEE802.3af compliant
powered device (PD) interface together with a PWM controller and support for auxiliary
sources.
Even though PM8800 can be configured to work in both isolated and non-isolated
topologies, this application note focuses on an isolated topology only, in two different output
power configurations (10 W and 20 W) and 2 different output voltages (5 V and 3.3 V).
The PM8800 demonstration kit supports diode as well as synchronous rectification.
Auxiliary sources can be connected to the board on 2 input points. One input allows
prevalence of the auxiliary sources with respect to the PoE, while the other input allows the
usage of a wall adaptor with voltage lower than the internal PoE UVLO threshold and still
benefits from the inherent inrush and DC current limit.
The above mentioned configurations are all supported by the PM8800 demonstration kit as
options on the same PCB. The bill of material (BOM) (see
Section 5 on page 12)
provides
the list of components to be mounted for each of the targeted configurations.
Figure 1.
PM8800 demonstration kit
The high-power board appears on the left of the photo and standard board is on the right.
September 2008
Rev 2
1/47
www.st.com
Contents
AN2783
Contents
1
2
3
4
Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Demonstration kit schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1
4.2
Input/output connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5
6
7
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Power-up sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Input section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.1
7.2
7.3
Diode bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Input capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Transient voltage suppression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8
PoE section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1
8.2
8.3
8.4
8.5
8.6
8.7
Signature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
UVLO and power-on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Inrush current limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
DC current limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
AUXI input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
AUXII input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
9
10
Power transformer and operating input voltage . . . . . . . . . . . . . . . . . . 22
Power converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
10.1
10.2
10.3
Flyback continuous conduction mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Main switch current and current sensing . . . . . . . . . . . . . . . . . . . . . . . . . 24
Main switch power dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2/47
AN2783
Contents
10.4
10.5
Rectifier diode dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
PM8800 internal power dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
11
12
Layout guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
12.1
12.2
12.3
12.4
Efficiency measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5 V high-power board measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.3 V standard-power board measurements . . . . . . . . . . . . . . . . . . . . . . 36
IEEE 802.3af compatibility test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Appendix A Schematic of high-power board . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Appendix B Schematic of standard-power board . . . . . . . . . . . . . . . . . . . . . . . . 45
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3/47
List of figures
AN2783
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.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.
Figure 37.
Figure 38.
Figure 39.
Figure 40.
Figure 41.
Figure 42.
Figure 43.
Figure 44.
Figure 45.
Figure 46.
Figure 47.
Figure 48.
PM8800 demonstration kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Demonstration kit schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Assembly view: top and bottom layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Top layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Inner layer 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Inner layer 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Bottom layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Inrush current limit vs. RIRL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
DC current limit vs. RDC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Output power vs. VAUXII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5 V out - standard board with diode rectification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5 V out - high-power board with synchronous rectification . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.3 V out - standard board with diode rectification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.3 V out - high-power board with synchronous rectification . . . . . . . . . . . . . . . . . . . . . . . 30
Startup of the PM8800 demonstration kit with 5 V 1 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Startup of the PM8800 demonstration kit with 5 V 4 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Details of the inrush phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Details of the soft-start phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
VDS and VGS of the primary MOSFET for 5 V 1 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
VDS and VGS of the primary MOSFET for 5 V 4 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Details of the synchronous rectifier MOSFET voltage with 48 V and 4 A out . . . . . . . . . . 32
Output voltage ripple at 4 A output current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Output voltage ripple at 4 A output current (1 sec persistence) . . . . . . . . . . . . . . . . . . . . . 33
Dynamic load 1 A to 4 A: output voltage (up) and output current (down) . . . . . . . . . . . . . 33
PM8800A response to a 6 A overload condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
PM8800A recovering from a 6 A overload condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
PM8800A response to a short on the load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
PM8800A recovering from a short on the load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Internal short on the secondary winding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Switch between 48 V PoE and 24 V AUXII with 5 V at 2 A . . . . . . . . . . . . . . . . . . . . . . . . 35
back to 48 V removing the 24 V AUXII voltage with 5 V at 2 A . . . . . . . . . . . . . . . . . . . . . 35
Switch between 48 V PoE and 12 V AUXII with 5 V at 2 A . . . . . . . . . . . . . . . . . . . . . . . . 36
Back to 48 V removing the 12 V AUXII voltage with 5 V at 2 A . . . . . . . . . . . . . . . . . . . . . 36
Startup of the PM8800 demonstration kit with 3.3 V, 1 A . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Startup of the PM8800 demonstration kit with 3.3 V, 3 A . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Details of the inrush phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Details of the soft-start phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
VDS and VGS of the primary MOSFET for 3.3 V 1 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
VDS and VGS of the primary MOSFET for 3.3 V 3 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Details of the synchronous rectifier MOSFET voltage with 48 V and 3 A output current . . 38
Output voltage ripple at 3 A output current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Output voltage ripple at 3 A output current (1 sec persistence) . . . . . . . . . . . . . . . . . . . . . 38
Dynamic load 1 to 3 A: output voltage (up) and output current (down) . . . . . . . . . . . . . . . 39
PM8800A response to a 5 A overload condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
PM8800A recovering from a 5 A overload condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
PM8800A response to a short on the load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
PM8800A recovering from a short on the load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Internal short on the secondary winding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4/47
AN2783
Figure 49.
Figure 50.
Figure 51.
Figure 52.
Figure 53.
Figure 54.
List of figures
Switch between 48 V PoE and 24 V AUXII with 3.3 V at 2 A . . . . . . . . . . . . . . . . . . . . . . . 41
Back to 48 V removing the 24 V AUXII voltage with 3.3 V at 2 A . . . . . . . . . . . . . . . . . . . . 41
Switch between 48 V PoE and 12 V AUXII with 3.3 V at 2 A . . . . . . . . . . . . . . . . . . . . . . . 41
Back to 48 V removing the 12 V AUXII voltage with 3.3 V at 2 A . . . . . . . . . . . . . . . . . . . . 41
Schematic of the 3.3/5 Vout high power with synchronous rectification . . . . . . . . . . . . . . . 44
Schematic of the 3.3/5 Vout standard power with diode rectification . . . . . . . . . . . . . . . . . 45
5/47
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
