Application Notes

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Using the Inhibit Control of the PT5400

SWIFT™

Series of Power Modules

For applications requiring output voltage On/Off control,

the PT5400 series of SWIFT power modules incorporate

an inhibit function. This function can be used wherever

there is a requirement for the module to be switched

off. The On/Off function is provided by the Inhibit

(pin 1) control.

The ISR functions normally with Pin 1 open-circuit,

providing a regulated output whenever a valid source

ground signal is applied to pin 1, the regulator output

will be disabled.

Figure 3-1 shows an application schematic, which details

the typical use of the Inhibit function. Note the discrete

transistor (Q1). The Inhibit control has its own internal

control thresholds are given in Table 3-1.

Table 3-1; Inhibit Control Requirements

Parameter

Min

Max

Enable (VIH)Vin – 0.5

Open

Disable (VIL)

–0.2V

+0.5V

Notes:

1. Use an open-collector device (preferably a discrete

transistor) for the Inhibit input. A pull-up resistor is not

necessary. To disable the output voltage, the control pin

should be pulled low to less than +0.5VDC.

Figure 3-1

Turn-On Time:

on applies a low-voltage to the Inhibit control (pin 1)

and disables the regulator output. Correspondingly,

power up. The soft-start power up consists of a short

voltage rises from zero to its full regulation voltage.

(See the section on Soft-Start Power Up). The module

produces a fully regulated output voltage within 25msec.

Figure 3-2 shows the typical rise in both output voltage

and input current for a PT5404 (1.8V), following the

a 5Vdc input voltage, and 0.7-

Ω resistive load.

Figure 3-2

C

1

100

µF

+V

O

COM

+V

IN

COM

Inhibit

Q1

BSS138

PT5401

2

13

4

Vi n

Vo

GND

INH

d

t

Vout (1V/Div)

Iin (0.5A/Div)

HORIZ SCALE: 5ms/Div

Q1 Vgs (10V/Div)

PT5400 Series