Datasheet

LNK362-364
C
12/05
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 fi lter
capacitor to the area of copper connected to the SOURCE
pins.
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 fi lter
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 capacitor should be directly from
the primary input fi lter 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 fi lter is used, then the inductor in the
fi lter should be placed between the negative terminals of the
input fi lter capacitors.
Figure 6. Recommended Printed Circuit Layout for LinkSwitch-XT in a Flyback Converter Confi guration.
+
+
HV DC
INPUT
-
-
DC
OUT
TOP VIEW
PI-4155-102705
T
r
a
n
s
f
o
r
m
e
r
Input Filter
Capacitor
C
BP
Output Filter
Capacitor
D
S
S
FB
BP
S
S
Maximize hatched copper
areas ( ) for optimum
heatsinking
S
S
LinkSwitch-XT
Opto-
coupler
Y1-
Capacitor