On/Off Inhibit

V

I

Inhibit/

UVLO Prog

1=Inhibit

PTH04T240F

3

2

C

I

11

4

+

GND

UDG-08163

V

I

GND

V

V

I

T - Time - 4 ms/div

PTH04T240F

For applications requiring output voltage on/off control, the PTH04T240F 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 19 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 40

ms. Figure 20 shows the typical rise in both the output voltage and input current, following the turn-off of Q1. The

current load.

Figure 19. On/Off Inhibit Control Circuit

Figure 20. Power-Up Response from Inhibit Control

Copyright © 2008–2009, Texas Instruments Incorporated

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Product Folder Link(s): PTH04T240F