6

LNK362-364

2-6

Rev. E 11/08

6

Bypass Capacitor C

BP

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-XT together

should be kept as small as possible.

Primary Clamp Circuit

A clamp 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-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-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.

Optocoupler

Place the optocoupler physically close to the LinkSwitch-XT to

minimize the primary-side trace lengths. Keep the high current,

high-voltage drain and clamp traces away from the optocoupler

to prevent noise pick up.

Output Diode

For best performance, the area of the loop connecting the

secondary winding, the output diode and the output filter

+

+

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

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