FTM Board Club
STMicroelectronics
STEVAL-POE006V1
3.3V/20A, active clamp forward converter, Power Over Ethernet (PoE) IEEE 802.3bt compliant reference design

This reference design represents a 3.3 V, 20 A converter solution ideal for various applications including wireless access points, supplied with a PoE-PD interface and a DC-DC active clamp forward converter.

The PoE-PD interface is based on the PM8805 system in package device with two active bridges and an IEEE 802.3bt compliant Powered Device (PD) interface. It can be used in all medium-to-high power 2P and 4P high efficiency PoE and PoE+ applications.
The DC-DC active clamp forward converter is designed around the PM8804 PWM controller, which is an integrated solution for smart and efficient 48 V converters, featuring a programmable oscillator for the switching frequency, adjustable slope compensation, dual complementary low-side drivers with programmable dead time, programmable soft start, soft turn off and a programmable current sense blanking time.

Features
  • Features of the PM8805 PoE-PD interface:
    • System in package integrating a double active bridge, a hot-swap MOSFET and a PoE-PD
    • Supports legacy high power, 4-pair applications
    • 100 V N-ch MOSFETs with 0.2 Ω total path resistance for each active bridge
    • Identifies which kind of PSE (standard or legacy) it is connected to and provides successful IEEE 802.3af/at/bt classification indication as a combination of the T0, T1 and T2 signals (open drain)
    • Smart operation mode selection through the STBY, FAUX and RAUX control signals
    • QFN 56 8x8mm package with 43 pins and 6 exposed pads
  • Features of the PM8804 PWM controller:
    • PWM peak current mode controller
    • Input operating voltage up to 75 V
    • Internal high voltage start up regulator with 20 mA capability
    • Programmable fixed frequency up to 1 Mhz
    • Soft startup with settable time
    • Soft turn off (optionally disabled)
    • Dual 1 APK, low side complementary gate drivers
    • GATE2 can be turned off for reduced consumption
    • 80% maximum duty cycle with internal slope compensation
    • QFN 16 3x3mm package with exposed pad