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Overtemperature Protection (OTP)

Output On/Off Inhibit

PTH12060W

1

10

4

5

6

2

3

L

O

A

D

1 = Inhibit

GND

9

8

Q1

BSS138

7

GN D

R

2k

1%

0.1 W

SET

C

330 F

O

m

C

560 F

I

m

V

I

V

V

O

PTH12040W

SLTS237A–DECEMBER 2004–REVISED OCTOBER 2005

The PTH12020, PTH12030, and PTH12040 products have overtemperature protection. These products have an

on-board temperature sensor that protects the module’s internal circuitry against excessively high temperatures.

A rise in the internal temperature may be the result of a drop in airflow, or a high ambient temperature. If the

internal temperature exceeds the OTP threshold, the module’s Inhibit control is internally pulled low. This turns

the output off. The output voltage drops as the external output capacitors are discharged by the load circuit. The

recovery is automatic, and begins with a soft-start power up. It occurs when the the sensed temperature

decreases by about 10°C below the trip point.

Note: The overtemperature protection is a last resort mechanism to prevent thermal stress to the regulator.

Operation at or close to the thermal shutdown temperature is not recommended and reduces the long-term

reliability of the module. Always operate the regulator within the specified safe operating area (SOA) limits for

the worst-case conditions of ambient temperature and airflow.

For applications requiring output voltage on/off control, each series of the PTH family incorporates an output

Inhibit control pin. The inhibit feature can be used wherever there is a requirement for the output voltage from the

regulator to be turned off.

The power modules function normally when the Inhibit pin is left open-circuit, providing a regulated output

has its own internal pull-up to a potential of 5 V to 13.2 V (see footnotes to electrical characteristics table). The

input is not compatible with TTL logic devices. An open-collector (or open-drain) discrete transistor is

recommended for control.

Figure 11. Inhibit Control Circuit

Turning Q1 on applies a low voltage to the Inhibit control pin and disables the output of the module. If Q1 is then

turned off, the module executes a soft-start power-up sequence. A regulated output voltage is produced within 25

constant current load.

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