PM8803 layout guideline

AN3387

2/12

Doc ID 018735 Rev 1

1

PM8803 layout guideline

1.1

General guidelines for the PoE converter

The following general guidelines are valid for all the typical converter topologies used for

PoE/PoE+ converters.

The length of the interconnections between the following groups of components belonging

to the primary side of the converter must be kept as short as possible:

1.

Input ceramic capacitors

2.

Input side of the power transformer

3.

Power MOSFET and sense resistors

4.

Active clamp circuitry or snubber circuitry (if present)

The length of the interconnections between the following groups of components belonging

to the secondary side of the isolation must be kept as short as possible:

1.

Secondary rectifier diode(s), or synchronous rectifier MOSFET(s) and associated

driving circuitry

2.

Output side of the power transformer

3.

Output ceramic capacitors

Isolation/spacing, as required by applicable safety standards, must be assured between all

the rails/traces/planes at 48 V and between the primary and secondary side of the

converter.

1.2

Pin description of PM8803 device

Figure 2 gives an indication on how the PM8803 pins are distributed, while Table 1 provides

a detailed description of each pin.

Figure 2.

Detail of the PM8803 pin distribution