© 2013 Fairchild Semiconductor Corporation
3
FEBFDMQ8203_90W • Rev. 1.0.1
This user guide supports the evaluation kit for GreenBridge™ and shielded gate
PowerTrench
®
MOSFET applying to a Power Device (PD) of Power over Ethernet
(PoE). It should be used in conjunction with their datasheets as well as Fairchild’s
application notes and technical support team. Please visit Fairchild’s website at
www.fairchildsemi.com
.
1.
Introduction
This document describes the proposed solution for PoE++ PD that increases the
delivering power up to 90 W. It is designed to rectify a polarity of DC voltage from
Power Source Equipment (PSE) and then active clamp forward DC-DC converter steps
down a nominal input voltage 48 V
IN
to output voltage 3.3 V
OUT
in 300 kHz of the
switching frequency. To deliver 90 W power through a network cable, the power system
is composed with four-pair architecture, which PSE uses to deliver data and power to the
PD through both the spare pair and data pair in the network cable at the same time.
1.1.
Description
GreenBridge™ FDMQ8203 replaces the conventional diode bridge to reduce the power
dissipation caused by the large voltage drop of a diode bridge, resulting in a lower power
class power device. The small package size of MLP4.5x5 reduces PCB area and increases
power density. FDMC86102 100 V shielded gate PowerTrench® MOSFET for the hot
swap switch has the low conduction loss and the ruggedness due to the low R
DS(on)
and
wide safe operating area (SOA). The FDMS86200 150 V shielded gate PowerTrench
MOSFET reduces switching loss and conduction loss in the primary switch of the active
clamp forward topology because it has low FOM (R
DS(on)
x Qg). The FDMS8025S 30 V
shielded gate PowerTrench MOSFET is optimized for synchronous rectification because
it has the low R
DS(on)
and outstanding body diode performance.
Figure 1. Power diagram
