Datasheet

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Output On/Off Inhibit
Inhibit
GND
GND
R
SET
0.05 W
1%
C1
Ceramic
C2
Ceramic
PTH04070W
2
4
31
5
V
O
AdjGND
V
O
V
IN
47-µF
47-µF
V
I
= 5 V V
O
= 1.8 V
Inhibit
BSS138
Q1
6.65 k
L
O
A
D
t − 5 ms/div
V
O
(1 V/div)
I
I
(1 A/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
has its own internal pullup to V
I
potential. An open-collector or open-drain device is recommended to control this
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
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