www.ti.com

Output On/Off Inhibit

PTH08T230W

GND

GND

3

10

Q1

BSS138

1=Inhibit

Inhibit/

UVLO

C

I

V

I

V

I

2

t-Time=4ms/div

I (1 A/div)

I

V

(2V/div)

O

V

(2V/div)

INH

Remote Sense

PTH08T230W, PTH08T231W

SLTS265F – NOVEMBER 2005 – REVISED MAY 2007

For applications requiring output voltage on/off control, the PTH08T230/231W 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

Figure 22 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 22. On/Off Inhibit Control Circuit

Figure 23. 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 23 shows the typical rise in both the output voltage and input current, following the turn-off of Q1. The

current load.

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.

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 300mV.

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.

24

Submit Documentation Feedback

Copyright © 2005–2007, Texas Instruments Incorporated

Product Folder Link(s): PTH08T230W PTH08T231W