Datasheet

On/Off Inhibit
V
I
PTH08T240F
2
3
C
I
4
GND
+
GND
V
I
11
1=Inhibit
Q1
BSS 138
UDG-07130
T − Time − 4 ms/div
V
O
(1 V/div)
V
INH
(1 V/div)
I
I
(2 A/div)
PTH08T240F
SLTS277D – DECEMBER 2006 – REVISED MARCH 2009 ............................................................................................................................................... www.ti.com
For applications requiring output voltage on/off control, the PTH08T240F incorporates an 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 27 shows the typical application of the inhibit function. Note the discrete transistor (Q1). The Inhibit input
has its own internal pull-up. An external pull-up resistor should never be used with the inhibit pin. The input is not
compatible with TTL logic devices. An open-collector (or open-drain) discrete transistor is recommended for
control.
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 15
ms. Figure 28 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, V
INH
. The waveforms were measured with a 10-A constant
current load.
Figure 27. On/Off Inhibit Control Circuit Figure 28. Power-Up Response from Inhibit Control
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