Datasheet

Output On/Off Inhibit
Inhibit
GND GND
PTN78060
1
4
6
2
3
Adjust
GND
GND
V
O
V
I
V =12V
I
V =5V
O
Inhibit
7
5
Sense
+
L
O
A
D
C
I
2.2 Fm
Ceramic
R
SET
21kW
0.05W
1%
C
O
100 Fm
Q1
BSS138
PTN78060W , PTN78060H
SLTS229B – NOVEMBER 2004 – REVISED JUNE 2009 ................................................................................................................................................... www.ti.com
To use the output voltage sense feature, simply connect the V
O
Sense input (pin 5) to V
O
, close to the device
that draws the most supply current. If an external voltage sense is not desired, the V
O
Sense input may be left
open circuit. An internal resistor (15 Ω or less), connected between this input and V
O
, ensures that the output
remains in regulation.
With V
O
Sense connected, the difference between the voltage measure directly between the V
O
and GND, and
that measured from V
O
Sense to GND, represents the amount of IR-voltage drop being compensated by the
regulator. This should be limited to a maximum of 0.3 V.
Note:The external voltage sense is not designed to compensate for the forward drop of nonlinear or
frequency-dependent components that may be placed in series with the regulator's output. Examples include
OR-ing diodes, filter inductors, ferrite beads, and fuses. When these components are enclosed by the external
sense connection, they are effectively placed inside the regulation control loop. This can adversely affect the
stability of the module.
The inhibit feature can be used wherever there is a requirement for the output voltage to be turned off. The
power module functions normally when the Inhibit control (pin 3) is left open-circuit, providing a regulated output
whenever a valid source voltage is connected to V
I
with respect to GND. Figure 30 shows the the circuit used to
demonstrate the inhibit function. Note the discrete transistor (Q1). Turning Q1 on applies a low voltage to the
Inhibit control pin and turns the module off. The output voltage decays as the load circuit discharges the
capacitance. The current drawn at the input is reduced to typically 17 mA. If Q1 is then turned off, the module
executes a soft-start power up. A regulated output voltage is produced within 20 ms. Figure 31 shows the typical
rise in the output voltage, following the turn off of Q1. The turn off of Q1 corresponds to the fall in the waveform,
Q1 Vgs. The waveforms were measured with a 2.8-A resistive load.
Figure 30. On/Off Inhibit Control Circuit
18 Submit Documentation Feedback Copyright © 2004 – 2009, Texas Instruments Incorporated
Product Folder Link(s): PTN78060W PTN78060H