Main characteristics and circuit description

AN4377

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Main characteristics and circuit description

The main characteristics (reference and electrical specifications) of the converter are listed

in Table 2.

This document details the characteristics and performances of the PM8800A demonstration

kit STEVAL-TSP005V2 which has been designed to cover a broad range of power over

ethernet (PoE) applications.

The PM8800A is a highly integrated device embedding an IEEE 802.3af compliant powered

device (PD) interface together with a PWM controller and support for auxiliary sources.

Even though the PM8800A can be configured to work in both isolated and non-isolated

topologies, single or double output; this application note focuses on a low cost isolated

flyback converter topology with diode rectification, 5 V output voltage with up to a 2 A output

current capability.

Auxiliary sources can be connected to the board on 2 input connectors. One input (AUX II)

allows prevalence of the auxiliary sources with respect to the PoE, while the other input

(AUX I) 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 PM8800A demonstration kit

as options on the same PCB. The bill of material (BOM) in Table 3 provides the list of

components to be mounted to obtain the 5 V at 2 A demonstration board.

Table 1. Reference

Reference code

Device

PM8800A

Demonstration board

STEVAL-TSP005V2

Table 2. Electrical specification

Parameter

Specifications

From 40 to 60 V at 13 W

5 Vdc ± 5 % at 2 A

Peak-to-peak output ripple

30 mV (120 mV without L4 output filter)

Efficiency DC-DC full load

> 86%

Efficiency overall peak

> 84%

Transient response

Voutpk to 50% load step

< 300 mV

V in load line case

< 0.5%

GLOOP bandwidth

5 kHz

GLOOP phase margin at 0 dB

70 deg.

GLOOP dB margin at 0 deg.

-10 dB