Datasheet
Output On/Off Inhibit
GND
2
3
+
GND
Inhibit/
UVLO
1 = Inhibit
Q1
BSS138
10
V
I
V
I
C
I
UDG−06045
PTH04T260/261W
T − Time − 10 ms/div
V
O
(1 V/div)
I
I
(1 A/div)
V
INH
(2 V/div)
Overcurrent Protection
PTH04T260W , PTH04T261W
SLTS273E – SEPTEMBER 2006 – REVISED JULY 2009 ..................................................................................................................................................
www.ti.com
For applications requiring output voltage on/off control, the PTH04T260/261W incorporates an output 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 21 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 should never be connected to the inhibit pin. The input is not
compatible with TTL logic devices. An open-collector (or open-drain) discrete transistor is recommended for
control.
Figure 21. On/Off Inhibit Control Circuit Figure 22. Power-Up Response from Inhibit 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 40
ms. Figure 22 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 3-A constant
current load.
For protection against load faults, all modules incorporate output overcurrent protection. Applying a load that
exceeds the regulator's overcurrent threshold causes the regulated output to shut down. Following shutdown, a
module periodically attempts to recover by initiating a soft-start power-up. This is described as a hiccup mode of
operation, whereby the module continues in a cycle of successive shutdown and power up until the load fault is
removed. During this period, the average current flowing into the fault is significantly reduced. Once the fault is
removed, the module automatically recovers and returns to normal operation.
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