Layout guidelines

PM8804

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DocID031629 Rev 1

6.2

How to layout the PM8804 ground pins

PM8804 is provided with two different pins of ground AGND and PGND plus an exposed

pad.

The exposed pad must be connected to AGND and is recommended a fill area with at least

a matrix of 3 x 3 vias to AGND plane.

Increase the number of AGND power planes helps improve the heat dissipation and it is

recommended under the PM8804.

Is recommended to use a wide power copper plane for AGND connection and when is

possible avoid to use traces.

The board ground must be separated into PGND and AGND: pin 11 and pin 9 must be

referred to PGND; all other circuitry and all others components must be connected to

AGND.

The AGND must be connected to PGND in one point only, and it has to be as much as

possible close to the pin10.

It is recommended to use a small copper area for the PGND.

AGND can be a wide copper plane connecting the several components referred to it.

On secondary side is recommend to keep separated the power path of the power secondary

GND (output side of transformer, secondary rectifier, output capacitors) from the feedback

network GND, which will be connected only at the output capacitors side.

The low potential of PoE/48V voltage can be routed with a wide trace at the input and along

the input filter, to become a copper plane close to the PM8804.

6.3

Thermal aspects



Design the primary MOSFET area with at least 6 - 9 vias of connection to the internal

copper area.



Increase where possible the number of connected power planes, at least below the

MOSFETs and diodes to improve the heat dissipation.



Design the secondary rectifier area with at least 6 - 9 vias of connection to the internal

copper area.



The Thermal copper area has to be sized taking into account the thermal reason and

its impact on EMI when placed under switching devices like power MOSFETs and

diodes.