LNK362-364

B

11/05

6

LinkSwitch-XT

Layout Considerations

See Figure 6 for a recommended circuit board layout for

LinkSwitch-XT

.

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

BP

TheBYPASSpincapacitorshouldbelocatedasnearaspossible

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-XT together

should be kept as small as possible.

Primary Clamp Circuit

Aclamp is 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-XT

.

Thermal Considerations

The copper area underneath the LinkSwitch-XT acts not only

as a single point ground, but also as a heatsink. As this area is

connected to the quiet source node, it should be maximized for

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

cathode of the output diode.

Y Capacitor

The placement of the Y capacitor 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-XT device. Note that if an

input pi (C, L, C) EMI filter is used, then the inductor in the

filter should be placed between the negative terminals of the

input filter capacitors.

Figure 6. Recommended Printed Circuit Layout for LinkSwitch-XT in a Flyback Converter Configuration.

+

+

HV DC

INPUT

-

-

DC

OUT

TOP VIEW

PI-4155-102705

T

r

a

n

s

f

o

r

m

e

r

Input Filter

Capacitor

Output Filter

Capacitor

D

S

S

FB

BP

S

S

Maximize hatched copper

areas (

) for optimum

heatsinking

S

S

Opto-

coupler

Y1-

Capacitor