Datasheet

PTH08T260W
2
3
+
GND
GND
1 = Inhibit
10
Q1
BSS138
UDG−06082
V
I
V
I
C
I
t-Time=4ms/div
I (0.5 A/div)
I
V (2V/div)
O
V (2V/div)
INH
PTH08T260W, PTH08T261W
www.ti.com SLTS272G –DECEMBER 2006– REVISED AUGUST 2011
Output On/Off Inhibit
For applications requiring output voltage on/off control, the PTH08T260/261W 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 20 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 20. On/Off Inhibit Control Circuit Figure 21. 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 15
ms. Figure 21 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.
Remote Sense
Differential remote sense improves the load regulation performance of the module by allowing it to compensate
for any IR voltage drop between its output and the load in either the positive or return path. An IR drop is caused
by the output current flowing through the small amount of pin and trace resistance. Connecting the +Sense (pin
5) and –Sense (pin 6) pins to the respective positive and ground reference of the load terminals improves the
load regulation of the output voltage at the connection points.
With the sense pins connected at the load, the difference between the voltage measured directly between the V
O
and GND pins, and that measured at the Sense pins, is the amount of IR drop being compensated by the
regulator. This should be limited to a maximum of 300 mV.
If the remote sense feature is not used at the load, connect the +Sense pin to V
O
(pin 4) and connect the –Sense
pin to the module GND (pin 3).
The remote sense feature is not designed to compensate for the forward drop of nonlinear or frequency
dependent components that may be placed in series with the converter output. Examples include OR-ing
diodes, filter inductors, ferrite beads, and fuses. When these components are enclosed by the remote sense
connection they are effectively placed inside the regulation control loop, which can adversely affect the
stability of the regulator.
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