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Copyright © 2009

Microsemi

Rev. 1.3 2009-02-23

Analog Mixed Signal Group

2381 Morse Avenue, Irvine, CA 92614, USA; Phone (USA): (800) 713-4113, (ROW): (949) 221-7100 Fax: (949) 756-0308

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This ground plane should be 1500Vrms isolated from

the PoE circuitry as well as the power supply for the

PoE circuitry. The digital and analog grounds are

electrically the same ground. However, in order to

reduce noise coupling, the grounds are physically

separated and connected only at a single point.

5V Regulator

A single port application includes a 5V regulator

(Vcc) fed by the Vmain through D1 and D3 Zener

diodes and provides up to 25 mA used to power the

CPU and peripheral components in the PoE domain.

Using a 3% accuracy power supply for the PoE

circuitry D1 and D3 should be selected according to

the power supply nominal voltage set point using the

following graph.

D1 voltage plus D3 voltage as seen in the below

graph, should be evenly divided between the two

Zener diodes.

If an adequate 5V power source is available, the 5V

regulation circuitry can be removed and the Zener

diodes may be replaced with lower current (5 mA)

Zener diodes but with same voltage requirements.

Detailed Application

Description____________

(See Figure 2)

The PD64001/H performs a multitude of internal

operations and PoE functions, requiring a bare

minimum of external components.

The device is based on Atmel's ATtiny461 MCU.

Each PD64001/H device handles one port. Figure 2

shows the device with its related components for a

1-port configuration.

Mode Configuration - set by the resistor divider

(R7/R8) tied in to the RMODE line. The values are

fixed for each mode of operation and described in

the "R Mode pin" section in this document.

Line Detection Circuitry – when performing a line

detection procedure, the PoE device utilizes certain

voltage levels over the output port. These levels are

produced by switched resistor dividers and sensed

by the PD64001/H in order to confirm a valid PD

connection.

Current Loop Circuitry – the current is controlled by

Q4 MOSFET. The PD64001/H provides PWM signal

via pin#2 with a constant duty cycle (depending on

the R mode configuration). This PWM signal is

filtered and utilized as the current limit circuitry

voltage reference.

Sense Resistors – for each powered port, two

2-Ohm 2010 (1%) resistors connected in parallel

(1-Ohm equivalent) are used in series with the

output (R9, R11). In cases where the ambient

temperature drops below 70

not have to meet 802.3at power, a single 1-Ohm

2010 (1%) resistor is adequate.

Classification Circuitry – Upon port investigation

completion, the PD should be classified by its

classification current signature. Two voltage levels

are set over the port, derived from a reference

voltage filtered from PD64001/H's pin#4 (PWM

signal) and sent to an operational amplifier

controlling Q4.

Output port - The load resistance of the PD attached

to the port is presented in parallel with R13.

The resulting voltage developed across both

resistances is monitored to establish the 802.3af/at

compatibility.

LED indication - The 1 port application may use the

PD64001/H LED1 and LED2 pins for system status

indications as shown below:

R30 20K

PD-1206

R31 1K

Vmain

R33 1K

LED2

LED1

D10

Vcc

Vmain_OK