TNY375-380
Maximize hatched copper
Return bias winding
directly to input capacitor
Safety Spacing
Copper area for
heat sinking
areas (
) for optimum
heat sinking
Y1-
Capacitor
Output
Rectiꢀer
+
High-Voltage
-
Input Filter Capacitor
PRI
T
r
a
n
s
f
o
r
m
e
r
SEC
BIAS
PRI
D
S
S
S
S
BP/M
BIAS
TOP VIEW
EN/UV
CBP
Opto-
coupler
RUV
DC
-
+
OUT
Route connections to EN/UV pin
(including undervoltage resistor)
away from drain connected traces
Bypass capacitor connection
to device should be short
PI-4675-090712
Figure 16. Layout Considerations for TinySwitch-PK Using P Package.
Y-Capacitor
1. Maximum drain voltage – Verify the VDS does not exceed
6ꢀ0 V at highest input voltage and peak (overload) output
power. The ꢀ0 V margin to the 700 V BVDSS specification
gives margin for design variation.
2. Maximum drain current – At maximum ambient temperature,
maximum input voltage, and peak output (overload) power,
verify drain current waveforms for any signs of transformer
saturation and excessive leading edge current spikes at
startup. Repeat under steady state conditions and verify that
the leading edge current spike event is below IINIT at the end
of the tLEB(Min). Under all conditions the maximum drain
current should be below the specified absolute maximum
ratings.
3. Thermal Check – At specified maximum output power,
minimum input voltage, and maximum ambient temperature,
verify that the temperature specifications are not exceeded
for TinySwitch-PK device, transformer, output diode, and
output capacitors. Enough thermal margin should be allowed
for part-to-part variation of the RDS(ON) of TinySwitch-PK device
as specified in the data sheet. Under low-line maximum
power, a maximum TinySwitch-PK device SOURCE pin
temperature of 110 °C is recommended to allow for these
variations.
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-PK 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 on the input filter capacitors.
Optocoupler
Place the optocoupler physically close to the TinySwitch-PK
device 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
Capacitor should be minimized. In addition, for axial diodes,
sufficient copper area should be provided at the anode and
cathode terminal of diode for heat sinking. A larger area is
preferred at the quiet cathode terminal. A large anode area can
increase high frequency radiated EMI.
Quick Design Checklist
Design Tools
As with any power supply design, all TinySwitch-PK designs
should be verified on the bench to make sure that component
specifications are not exceeded under worst case conditions.
The following minimum set of tests is strongly recommended:
Up-to-date information on design tools can be found at the
Power Integrations web site: www.powerint.com.
11
www.powerint.com
Rev. C 09/12
POWERINT [ Power Integrations ]
