Application Notes

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PT6360 Series

Using the Inhibit Control of the PT6360 Series of

Integrated Switching Regulators

The PT6360 series of integrated switching regulators

(ISRs) provide step-down voltage conversion for output

loads of up to 11 A. For applications that require the

output voltage to be held off, these ISRs incorporate an

Inhibit* control (pin 1). The Inhibit* control input can be

used for power-up sequencing or whenever there is a

requirement for the output voltage from the ISR to be

turned off.

The ISR functions normally with pin 1 open circuit,

providing a regulated output whenever a valid source

5–8). When a low-level ground signal is applied to pin 1,

Figure 4-1 shows the typical application of the Inhibit*

open-collector or open-drain device is recommended to

Table 4-1.

Table 4-1; Inhibit Control Requirements

Parameter

Min

Typ

Max

Enable (VIH)

2.0 V

—

Vin

Disable (VIL)

–0.1 V

—

+0.3 V

I IL

—

–0.5 mA

—

Notes:

1. Use an open-collector device with a breakdown voltage

of at least 20 V (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 +0.6 VDC.

2. When a ground signal is applied to the Inhibit* control

(pin 1) the module output is effectively turned off (tri-

state). The output voltage decays to zero as the load

impedance discharges the output capacitors.

3. When a ground signal to the Inhibit* pin is removed,

the regulator output initiates a soft-start cycle by first

asserting a low impedance to ground. If an external

voltage is applied to the regulator output it will sink

current and possibly overstress the module.

4. When a ground signal is applied to the Inhibit* pin, the

module is effectively turned off and the input current is

reduced to about 0.5 mA.

Figure 4-1

Turn-On Time:

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

consists of a short delay (approx. 10 msec), followed by a

period in which the output voltage rises to the full regu-

lation voltage. The module produces a regulated output

voltage in approximately 15 msec. Figure 4-2 shows the

rise in both the output voltage and input current for a

The waveforms were measured with a 12 VDC input

voltage, and 8.3-A load.

Figure 4-2

PT6363

V

IN

5–8

12

9–10

2–4

1

L

O

A

D

C

IN

560 µF

C

OUT

330 µF

Inhibit

GND

GND

V

OUT

11

+V

SENSE

Q

1

BSS138

Vo (1V/Div)

Iin (2A/Div)

Q1 Vds (10V/Div)

HORIZ SCALE: 5ms/Div