PTH12030W/L
www.ti.com
SLTS211F–MAY 2003–REVISED FEBRUARY 2007
OUTPUT ON/OFF INHIBIT
For applications requiring output voltage on/off control, each series of the PTH family 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 VI with respect to GND.
Figure 12 shows the typical application of the inhibit function. Note the discrete transistor (Q1). The Inhibit input
has its own internal pull-up to a potential of 5 V to 13.2 V (see footnotes to specification table). The input is not
compatible with TTL logic devices. An open-collector (or open-drain) discrete transistor is recommended for
control.
VOSense
10
9
8
5
Q1V (5 V/div)
DS
VI
VO
2
6
PTH12060W
3 1
7
4
+
+
V (2 V/div)
O
L
CI
RSET
CO
O
A
D
560 mF
1 = Inhibit
GND
Q1
BSS138
2 kW
0.1 W
1 %
330 mF
GND
I (2 V/div)
I
t − Time − 10 ms/div
Figure 13. Power-Up from Inhibit Control
Figure 12. Inhibit Control Circuit
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
25 ms Figure 13 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, Q1 Vds. The waveforms were measured with a 5-A
constant current load.
REMOTE SENSE
Products with this feature incorporate an output voltage sense pin, VO Sense. A 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. An IR drop is caused by the high output current flowing through the small amount of pin and trace
resistance.
To use this feature simply connect the VO Sense pin to the VO node, close to the load circuit (see standard
application circuit). If a sense pin is left open-circuit, an internal low-value resistor (15-Ω or less) connected
between the pin and and the output node, ensures the output remains in regulation.
With the sense pin connected, the difference between the voltage measured directly between the VO and GND
pins, and that measured from VO Sense to GND, is the amount of IR drop being compensated by the regulator.
This should be limited to a maximum of 0.3 V.
Note: 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.
14
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