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Output On/Off Inhibit

Inhibit

GND

GND

0.05 W

1%

C1

Ceramic

C2

Ceramic

PTH04070W

2

4

3

1

5

GND

47-

µF

47-

µF

Inhibit

BSS138

Q1

6.65 k

L

O

A

D

t − 5 ms/div

Q1, Vgs (10 V/div)

PTH04070W

SLTS227B – SEPTEMBER 2004 – REVISED OCTOBER 2007

For applications requiring output voltage on/off control, the PTH04070W power module incorporates an output

on/off Inhibit control (pin 5). The inhibit feature can be used wherever there is a requirement for the output

voltage from the regulator to be turned off.

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

whenever a valid source voltage is connected to Vin with respect to GND.

Figure 11 shows the typical application of the inhibit function. Note the discrete transistor (Q1). The Inhibit control

input.

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 will execute a soft-start power-up sequence. A regulated output voltage is produced within

20 msec. Figure 12 shows the typical rise in the output voltage, following the turn off of Q1. The turn off of Q1

corresponds to the fall in the waveform, Q1 Vgs. The waveforms were measured with a 2-A resistive load.

Figure 11. On/Off Inhibit Control Circuit

Figure 12. Power Up Response From Inhibit Control

12

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