TNY274-280
Input Filter
Capacitor
TOP VIEW
Y1-
Capacitor
+
HV DC
INPUT
-
T
r
a
n
s
f
o
r
Output Filter
Capacitor
S
S S S
C
BP
m
e
r
TinySwitch-III
EN/UV BP/M D
Opto-
coupler
DC
OUT
+
-
Maximize hatched copper
areas (
) for optimum
heatsinking
PI-4278-013006
Figure 15. Recommended Circuit Board Layout for TinySwitch-III with Under-Voltage Lock Out Resistor.
Thermal Considerations
Optocoupler
The four SOURCE pins are internally connected to the IC lead
frameandprovidethemainpathtoremoveheatfromthedevice.
ThereforealltheSOURCEpinsshouldbeconnectedtoacopper
area underneath the TinySwitch-III to act not only as a single
point ground, but also as a heatsink. As this area is connected
to the quiet source node, this area should be maximized for
good heatsinking. Similarly for axial output diodes, maximize
the PCB area connected to the cathode.
Place the optocoupler physically close to the TinySwitch-III
to minimizing 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
capacitor, should be minimized. In addition, sufficient copper
area should be provided at the anode and cathode terminals
of the diode for heatsinking. A larger area is preferred at the
quiet cathode terminal. A large anode area can increase high
frequency radiated EMI.
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 TinySwitch-III device. Note – if an input π (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.
E
2/06
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POWERINT [ Power Integrations ]
