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IEEE 802.3bt compliant Power over Ethernet (PoE) interface reference design

STEVAL-POE001V1

Overview

This reference design integrates a high power standard PoE-PD interface compliant with the third generation IEEE 802.3bt PoE standard, able to support applications up to 100 W.

The PoE-PD interface is based on the PM8805 system in package featuring two embedded active bridges with driving circuitry, a charge pump to drive the high side MOSFETs, a hot swap MOSFET and a standard single-signature interface compliant with IEEE 802.3bt, including detection, classification, UVLO and inrush current limitation.
The device implements IEEE 802.3bt physical layer classification schemes to signal successful PSE type identification to the system: it identifies a 4-pair PSE by monitoring the Ethernet cable pairs and providing the system with a dedicated matrix of Tx signals.
The PM8805 is suitable for building the interface for PoE switch mode power supplies for maximum conversion efficiency, with a PGD signal that can be used to enable downstream DC-DC converters or LED drivers with suitable electrical parameters.

Main features

System in package including a dual active bridge, a hot swap MOSFET and a PoE-PD interface
Robust 100V N-ch MOSFETs with 0.2 Ω total path resistance for each active bridge
Robust 100 V, 0.1 Ω high side N-ch hot swap MOSFET
PoE-PD single-signature interface compliant with IEEE 802.3bt
Detection and support of high power, 4-pair applications
Identifies which kind of PSE (standard or legacy) it is connected with, and provides successful IEEE 802.3af/at/bt classification indication through combination of the T0, T1 and T2 signals (open drain)
Programmable classification current with 3.3 ms delay

Advanced energy-saving MPS timings
Two step hot swap current protection: DC with 1 ms delay and overload with 10 µs delay
Startup phase (pre-charge of the output capacitor), performed using an internally limited current source
PGD signal (open drain) to enable an external PWM controller
Thermal shutdown protection
RoHS compliant
WEEE compliant

Design Files

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Update:2025-06-20 13:48:41

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