Datasheet
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Output On/Off Inhibit
PTV08040W
6,7
13,14
20,21
4 5 11
V
I
V
I
C
I
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
SLTS257B – SEPTEMBER 2005 – REVISED JANUARY 2008
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
whenever a valid source voltage is connected to V
I
with respect to GND.
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. The
turn off of Q1 corresponds to the rise in the waveform, Q1 V
DS
. The waveforms were measured with a 20-A
constant current load.
Figure 14. Power-Up Response from Inhibit Control
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