TNY253/254/255
Safety Spacing
Input Filter Capacitor
+
HV
–
S
D
Transformer
Output Filter Capacitor
PRI
SEC
TOP VIEW
TinySwitch
Y1-
Capacitor
–
C
BP
BP
S
EN
DC
+
OUT
Opto-
coupler
Maximize hatched copper
areas (
) for optimum
heat sinking
PI-2176-071398
Figure 13. Recommended PC Layout for the TinySwitch.
easily accommodated by rating the output diode to handle the
short-circuit current. The short-circuit current can be minimized
by choosing the smallest (lowest current limit) TinySwitch for
the required power.
Layout
Single Point Grounding
Use a single point ground connection at the SOURCE pin for
the BYPASS pin capacitor and the Input Filter Capacitor (see
Figure 13).
Primary Loop Area
The area of the primary loop that connects the input filter ca-
pacitor, transformer primary and TinySwitch together, should
be kept as small as possible.
Primary Clamp Circuit
A clamp or snubber circuit is used to minimize peak voltage
and ringing on the DRAIN pin at turn-off. This can be achieved
by using an RC snubber for less than 3 W or an RCD clamp
as shown in Figure 13 for higher power. A Zener and diode
clamp across the primary or a single 550 V Zener clamp from
DRAIN to SOURCE can also be used. In all cases care should
be taken to minimize the circuit path from the snubber/clamp
components to the transformer and TinySwitch.
Thermal Considerations
Copper underneath the TinySwitch acts not only as a single
point ground, but also as a heatsink. The hatched area shown
in Figure 13 should be maximized for good heat-sinking of
TinySwitch and output diode.
Y Capacitor
The placement of the Y capacitor should be directly from the
primary single point ground to the common/return terminal on
the secondary side. Such placement will maximize the EMI
benefit of the Y capacitor.
Optocoupler
It is important to maintain the minimum circuit path from
the optocoupler transistor to the TinySwitch ENABLE and
SOURCE pins to minimize noise coupling.
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. See Figure 13 for optimized
layout. In addition, sufficient copper area should be provided
at the anode and cathode terminals of the diode to adequately
heatsink the diode under output short-circuit conditions.
Input and Output Filter Capacitors
There are constrictions in the traces connected to the input and
output filter capacitors. These constrictions are present for two
reasons. The first is to force all the high frequency currents
to flow through the capacitor (if the trace were wide then it
could flow around the capacitor). Secondly, the constrictions
minimize the heat transferred from the TinySwitch to the input
filter capacitor and from the secondary diode to the output filter
capacitor. The common/return (the negative output terminal
in Figure 13) terminal of the output filter capacitor should be
connected with a short, low resistance path to the secondary
winding. In addition, the common/return output connection
should be taken directly from the secondary winding pin and
not from the Y capacitor connection point.
Rev E
02/12
9
POWERINT [ POWER INTEGRATIONS, INC. ]
