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Output On/Off Inhibit
V
I
L
O
A
D
1= Inhibit
GND
GND
V
O
Q1
BSS138
R
SET
2.21kW
C1 C3C2
PTV03010W
V
I
V
O
GND
GND
Inhibit
V Adj
O
Track
t-Time=5ms/div
V (1V/div)
O
I (5 A/div)
I
Q1V (5V/div)
DS
PTV03010W
SLTS241A – FEBRUARY 2005 – REVISED JULY 2007
For applications requiring output voltage on/off control, the modules incorporate an output Inhibit control. 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 input is left open-circuit, providing a regulated output
whenever a valid source voltage is connected to V
I
with respect to GND.
Figure 9 shows the typical application of the inhibit function. Note the discrete transistor (Q1). The Inhibit input
has its own internal pullup (see footnotes to electrical characteristics table). The input is not compatible with TTL
logic devices. An open-collector (or open-drain) discrete transistor is recommended for control.
Figure 9. On/Off Inhibit Application Circuit
Turning Q1 on applies a low voltage to the Inhibit control 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 10 shows the typical rise in both the output voltage and input current, following the turnoff of Q1.
The turnoff of Q1 corresponds to the rise in the waveform, Q1 V
DS
. The waveforms were measured with a 5-A
constant current load.
Figure 10. Inhibit Waveform
11
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