Layout hints

AN2755

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Layout hints

The layout of any converter is a very important phase in the design process that sometimes

does not have enough attention from the engineers. Even if it the layout phase sometimes

looks time-consuming, a good layout does save time during the functional debugging and

the qualification phases. Additionally, a power supply circuit with a correct layout needs

smaller EMI filters or less filter stages which allows consistent cost savings.

The L6562A does not need any special attention to the layout, just the general layout rules

for any power converter have to be carefully applied. Basic rules are listed below, using the

EVL6562A-400W schematic as a reference. They can be used for other PFC circuits having

any power level, working either in FOT or TM control.

1.

Keep power and signal RTNs separated. Connect the return pins of component-

carrying high currents such as C4, C5 (input filter), sense resistors, and C6, C7 (output

capacitors) as close as possible. This point is the RTN star point. A downstream

converter must be connected to this return point.

2.

Minimize the length of the traces relevant to L3, boost inductor L4, boost rectifier D4

and output capacitor C6 and C7.

3.

Keep signal components as close as possible to each L6562A relevant pin. Specifically,

keep the tracks relevant to pin #1 (INV) net as short as possible. Components and

traces relevant to the error amplifier have to be placed far from traces and connections

carrying signals with high dv/dt like the MOSFET drains (Q1 and Q2).

4.

Connect heat sinks to power GND.

5.

Add an external shield to the boost inductor and connect it to power GND.

6.

Connect a ceramic capacitor (100 ÷ 470 uF) to pin #8 (Vcc) and to pin #6 (GND) and

close to the L6562A. Connect pin #6 (GND) to the RTN star point (see 1).

Figure 21.

EVL6562A-400W PCB layout (not 1:1 scaled)

 

PFC PRECONDITIO NER

USING L6562A FO T

PFC PRECONDITIO NER

USING L6562A FO T