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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

SLTS227 – SEPTEMBER 2004

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