PD671xxx - 8 / 12 / 24-Channel PoE AF and AT DIMM

Data Sheet (Non-confidential)

Copyright © 2009

Microsemi

Page 10

Rev. 1.0 / 17-March-10

Analog Mixed Signal Group

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

Enhanced Mode PD671xxx DIMM Block Diagram

Figure 8 illustrates the internal circuitry of the Enhanced Mode DIMM Master. PD69012 appears only in one of

the 12 port circuits.

Figure 8: PD67124M DIMM, Internal Block Diagram

Top Assembly Description

The following sections detail the top assembly

components.

Power Supply

The entire circuit is powered by a nominal 48 VDC

potential (Vmain can range from 44 to 57 VDC for

AF mode and 50 to 57 VDC for AT high power

mode).

3.3 VDC Regulator

Each of the PD69012 includes a 3.3 VDC regulator

(EXT_REG and 3_3Vout) for up to 6 mA. This

current is utilized for powering external components

in the PoE domain. There is an option of adding a

driver to this output to drive higher loads. Q1

provides up to 30 mA to the PoE controller and to

the opto-couplers in the interface circuit. The total

capacitance on the 3.3 VDC should be less then

4.7 uF (with and without an external driver).

Grounds

The overall circuit includes two physical ground

planes, analog and digital, which are electrically

connected at a single point on the motherboard

(see Figure 9 and Figure 10). This method, used

throughout the design, improves noise immunity

and coupling. Application note AN-132, Catalogue

Number 06-0010-080 provides further details about

this design technique.

Control Signals

Several control signals are utilized between the

switch and the PoE circuitry:

xReset_In:

Driven by the switch circuitry

to reset the PoE circuit.

xDISABLE_PORTS

: Driven by the

switch, to disable all PoE ports

immediately.

Indication Signals

Int_out:

Enables the Host CPU to

reduce the communication volume

whenever a PoE event masked by the

Host CPU occurs. The PoE Controller

sends an interrupt for indication.

System_ok: (Enhanced mode only)

An

optional hardware single line, driven by

the Master DIMM to the Host CPU; this

signal provides the Host CPU with a

warning that a major failure such as

Vmain out of range has occurred.