Rev. F 08/16

9

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TNY253/254/255

TNY253/254/255

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.

TOP VIEW

PI-2176-071398

Y1-

Capacitor

Opto-

coupler

CBP

D

EN

BP

TinySwitch

+

–

HV

+

– DC

OUT

Input Filter Capacitor

Output Filter Capacitor

Safety Spacing

Transformer

Maximize hatched copper

areas (

) for optimum

heat sinking

S

S

PRI

SEC