LCS702LG datasheet(9/30 Pages) POWERINT

9 / 30 page

Rev. G 05/15

LCS700-708

www.power.com

Bootstrap Circuit and HB Node Layout

Please refer to Figure 10. Note the location of the bootstrap diode,

capacitor, resistor, and the HB trace routing. The objective is to keep

them away from the small signal components and traces, such as the

feedback optocoupler. Do not unnecessarily increase the area of the

PCB traces on this node, because it will increase the dv/dt (capacitive)

coupling to low-voltage circuits.

Transformer Secondary

The transformer secondary pins, output diodes, and main output

capacitors should be positioned close together and routed with short

thick traces. This is critical for secondary current symmetry and to

minimize output diode inverse voltage stress. The use of ceramic

capacitors allows placement between the transformer secondary pins

and the output rectifier, producing a very tight layout. See Figure 11.

The secondary winding halves should be inter-twined together before

they are wound on the bobbin. This minimizes the leakage inductance

between them and greatly improves current symmetry and minimizes

output diode inverse voltage stress. For a 2-output design the

half-windings of a given output need to be intertwined.

Figure 9. Placement of B+ and B- High-Voltage Bypass Capacitors.

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LCS702LG Datasheet(PDF) 9 Page - Power Integrations, Inc.