AN3373 Datasheet, PDF (1/18 Pages) STMicroelectronics – PM8803 is a highly integrated device embedding

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. PM8803 FLY demonstration kit
April 2011
Doc ID 018626 Rev 1
1/18
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