AN3387

PM8803 layout guideline

Doc ID 018735 Rev 1

5/12

1.3

How to layout the PM8803 different ground pins

There are 4 different ground pins on the PM8803: VSS, RTN1, RTN2, and ARTN, plus the

exposed pad.

The exposed pad of the PM8803 must be connected to VSS: design a fill area with at least 6

vias to VSS plane. Try, where possible, to increase the number of VSS power planes

connected, at least below the PM8803 position, to improve the heat dissipation of the

PM8803.

RTN1 and RTN2 are power ground pins for GAT1 and GAT2 drivers respectively. These pins

are not internally connected together and therefore must be externally connected with a

wide, short connection at the same point of the board power ground, which, in the following

is called GND.

Use a wide power copper plane for such connections; avoid to use traces as much as

possible.

Board GND must be divided into power GND (to connect input caps, Rsense, PM8803 pin 4

and 9, SA auxiliary circuitry, isolation cap) and signal GND or ARTN (to connect the other

components around the PM8803, the circuitry powered by VC voltage, and the IC pin 8).

The signal GND must be connected to power GND in one point only, close to the PM8803

RTN pins 4 and 9.

Use large copper plane for the power GND, if possible foresee a layer completely dedicated

to this.

ARTN can be a small copper plane or a wide trace connecting the several components

referred to it.

On the secondary side keep separated the power path of the power secondary GND (output

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

which is connected only at the output capacitors side.

VSS is the low potential of PoE voltage; it can be routed with a wide trace, but close to the

PM8803 as it must become a copper plane, in order to dissipate the heat transferred

through the exposed pad of PM8803.