TNY174PN データシートの表示（PDF） - Power Integrations, Inc

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TNY174PN

TinySwitch-LT Family Energy Efficient, Offline Switcher with Enhanced Flexibility and Extended Power Range®

Power Integrations, Inc 

TNY174-180

+

HV

-

TOP VIEW

Input Filter Capacitor

D

S

S

BP/M

S

S

EN

CBP

Safety Spacing

Y1-

Capacitor

Maximize hatched copper

areas (

) for optimum

heatsinking

Output

Rectifier

Output Filter

Capacitor

PRI

T

BIAS

r

a

n

PRI

s

f

o

r

m

BIAS

e

r

SEC

Opto-

coupler

- DC +

OUT

PI-4779-073107

Figure 13. Recommended Circuit Board Layout for TinySwitch-LT with Undervoltage Lock Out Resistor.

Thermal Considerations

The four SOURCE pins are internally connected to the IC lead

frame and provide the main path to remove heat from the device.

Therefore all the SOURCE pins should be connected to a copper

area underneath the TinySwitch-LT 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.

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-LT 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.

Optocoupler

Place the optocoupler physically close to the TinySwitch-LT

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.

PC Board Leakage Currents

TinySwitch-LT is designed to optimize energy efficiency across

the power range and particularly in standby/no-load conditions.

Current consumption has therefore been minimized to achieve

this performance. The EN pin for example operates with very

low threshold current levels and it is therefore recommended

to limit parasitic currents into and out of the EN pin to levels

below 1 μA.

Parasitic leakage currents into the EN pin are normally well below

this 1μA level when PC board assembly is in a well controlled

production facility. However, high humidity conditions together

with board and/or package contamination, either from no-clean

flux or other contaminants, can reduce the surface resistivity

enough to allow parasitic currents >1 μA to flow into the EN

pin. These currents can flow from higher voltage exposed solder

pads close to the EN pin such as the BP/M pin solder pad.

If the contamination levels in the PC board assembly facility

are unknown, the application is open frame or operates in a high

10 A

08/07

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