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Output On/Off Inhibit

PTV08040W

6,7

13,14

20,21

4

5

11

16

Inhibit/

UVLO

GND

GND

1= Inhibit

Q1

BSS138

V

(2V/div)

INH

I (2 A/div)

I

t-Time=2ms/div

V

(1V/div)

O

PTV08040W

SLTS257A – SEPTEMBER 2005 – REVISED JANUARY 2007

For applications requiring output voltage on/off control, the PTV08040W 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

Figure 13 shows the typical application of the inhibit function. Note the discrete transistor (Q1). The Inhibit input

has its own internal pull-up to a potential of 5 V. The input is not compatible with TTL logic devices. An

open-collector (or open-drain) discrete transistor is recommended for control.

Figure 13. On/Off 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 ms. Figure 14 shows the typical rise in both the output voltage and input current, following the turn-off of Q1.

constant current load.

Figure 14. Power-Up Response from Inhibit Control

16

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