Rev. H 11/08

6

LNK562-564

LinkSwitch-LP Layout Considerations

Layout

See Figure 6 for a recommended circuit board layout for

LinkSwitch-LP (P & G package).

Single Point Grounding

Use a single point ground connection from the input filter

capacitor to the area of copper connected to the SOURCE pins.

Bypass Capacitor (C

The BYPASS pin capacitor should be located as near as possible

to the BYPASS and SOURCE pins.

Primary Loop Area

The area of the primary loop that connects the input filter

capacitor, transformer primary and LinkSwitch-LP together

should be kept as small as possible.

Primary Clamp Circuit

An external clamp may be used to limit peak voltage on the

DRAIN pin at turn off. This can be achieved by using an RCD

clamp or a Zener (~200 V) and diode clamp across the primary

winding. In all cases, to minimize EMI, care should be taken

to minimize the circuit path from the clamp components to the

transformer and LinkSwitch-LP.

Thermal Considerations

The copper area underneath the LinkSwitch-LP acts not only as

a single point ground, but also as a heatsink. As it is connected

to the quiet source node, this area should be maximized for

good heat sinking of LinkSwitch-LP. The same applies to the

cathode of the output diode.

Y-Capacitor

The placement of the Y-type cap should be directly from the

primary input filter capacitor positive terminal to the common/

return terminal of the transformer secondary. Such a placement

will route high magnitude common-mode surge currents away

from the LinkSwitch-LP device. Note: If an input pi (C, L, C)

EMI filter is used, then the inductor in the filter should be placed

between the negative terminals on the input filter capacitors.

Figure 6. Recommended Circuit Board Layout for LinkSwitch-LP using P Package (Assumes a HVDC Input Stage).

+

HV DC

INPUT

-

+

Input Filter

Capacitor

-

DC

OUT

Output Filter

Capacitor

PI-4157-101305

Maximize hatched copper

areas (

) for optimum

heatsinking

TOP VIEW

Tr a n s f o r m e r

D

S

S

FB

BP

S

S