On/Off Inhibit

V

I

PTH08T240F

2

3

C

I

4

GND

+

GND

V

I

11

1=Inhibit

Q1

BSS 138

UDG-07130

T − Time − 4 ms/div

(1 V/div)

(1 V/div)

(2 A/div)

PTH08T240F

For applications requiring output voltage on/off control, the PTH08T240F incorporates an 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

Figure 27 shows the typical application of the inhibit function. Note the discrete transistor (Q1). The Inhibit input

has its own internal pull-up. An external pull-up resistor should never be used with the inhibit pin. The input is not

compatible with TTL logic devices. An open-collector (or open-drain) discrete transistor is recommended for

control.

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 15

ms. Figure 28 shows the typical rise in both the output voltage and input current, following the turn-off of Q1. The

current load.

Figure 27. On/Off Inhibit Control Circuit

Figure 28. Power-Up Response from Inhibit Control

Copyright © 2006–2008, Texas Instruments Incorporated

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