LNK362-364
Input Filter
Capacitor
TOP VIEW
Y1-
Capacitor
FB
D
T
r
a
n
s
f
o
r
m
e
r
S
S
BP
S
S
+
-
HV DC
INPUT
S
S
CBP
Opto-
coupler
+
DC
OUT
Maximize hatched copper
areas (
) for optimum
-
heatsinking
Output Filter
Capacitor
PI-4155-102705
Figure 6. Recommended Printed Circuit Layout for LinkSwitch-XT using P Package in a Flyback Converter Configuration.
Bypass Capacitor CBP
good heat sinking of LinkSwitch-XT. The same applies to the
TheBYPASSpincapacitorshouldbelocatedasnearaspossible
to the BYPASS and SOURCE pins.
cathode of the output diode.
Y-Capacitor
Primary Loop Area
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
fromtheLinkSwitch-XTdevice. Notethatifaninputpi(C, L, C)
EMIfilterisused, thentheinductorinthefiltershouldbeplaced
between the negative terminals of the input filter capacitors.
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.
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.
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
Output Diode
For best performance, the area of the loop connecting the
secondary winding, the output diode and the output filter
2-6
6
6
Rev. E 11/08
POWERINT [ Power Integrations ]
