Datasheet

Output On/Off Inhibit
Inhibit
GND GND
L
O
A
D
1 4
52
3
GNDInh Adj
C
I
2.2 mF
Ceramic
Q1
BSS138
V
I
= 12 V
PTN78000W
V
I
V
O
V
O
= 5 V
C
O
100 mF
R
SET
21 kW
0.05 W
1%
t-Time=5ms/div
V
O
(2V/div)
I
I
(0.5 A/div)
Q1V
GS
(10V/div)
PTN78000W , PTN78000H
www.ti.com ...................................................................................................................................... SLTS230C – NOVEMBER 2004 – REVISED SEPTEMBER 2008
For applications requiring output voltage on/off control, the PTN78000 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 29 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 30 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 V
GS
. The waveforms were measured with a 1.5-A resistive load.
Figure 29. On/Off Inhibit Control Circuit
Figure 30. Power Up Response From Inhibit Control
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