Datasheet

Inhibit
GND GND
1%
(Ceramic)
PTN78020
1
4
62
3
AdjustGND
V
O
V
I
V
I
=12V
V
O
=5V
Inhibit
7
5
Sense
+
Q
1
BSS138
L
O
A
D
21k
C
I
2.2 Fm
C
O
330 Fm
R
SET
0.05W
t-Time=5ms/div
V
O
(2V/div)
I
I
(2 A/div)
Q1V
GS
(10V/div)
PTN78020W
PTN78020H
SLTS228C – DECEMBER 2004– REVISED AUGUST 2011 www.ti.com
Output On/Off Inhibit
For applications requiring output voltage on/off control, the PTN78020 power module incorporates an output
on/off Inhibit control (pin 3). 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 V
I
with respect to GND. Figure 27 shows the the circuit used to
demonstrate the inhibit function. Note the discrete transistor (Q1). Turning Q1 on applies a low voltage to the
Inhibit control pin and turns the module off. The output voltage decays as the load circuit discharges the
capacitance. The current drawn at the input is reduced to typically 17 mA. If Q1 is then turned off, the module
executes a soft-start power up. A regulated output voltage is produced within 20 ms. Figure 28 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 1.5-A resistive load.
Figure 27. On/Off Inhibit Control Circuit
Figure 28. Power Up Response From Inhibit Control
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