Application Notes

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PT6980 Series

Using the Standby Function on the PT6980

Series of Dual-Output Voltage Regulators

Both output voltages of the 23-pin PT6980 dual-output

converter may be disabled using the regulator’s ‘Standby’

function. This function may be used in applications that

require power-up/shutdown sequencing, or wherever there

is a requirement to control the output voltage On/Off status

with external circuitry.

The standby function is provided by the STBY* control

(pin 3). If pin 3 is left open-circuit the regulator operates

regulator outputs will be simultaneously disabled and the

input current drawn by the ISR will drop to a typical value

of 4mA. The standby control may also be used to hold-off

both regulator outputs during the period that input power is

applied.

The standby pin is ideally controlled using an open-collector

(or open-drain) discrete transistor (See Figure 1). The

the circuit parameters for this control input.

Parameter

Min

TYP

Max

—

—

Open circuit

–0.1V

—

—

—

—

—

–0.5mA

Notes:

1. The standby control input is

other devices that incorporate a totem-pole output drive. Use

only a true open-collector device, preferably a discrete bipolar

transistor (or MOSFET). To ensure the regulator output is

disabled, the control pin must be pulled to less than 0.4Vdc

with a low-level 0.5mA sink to ground.

2 The standby control input requires no external pull-up resistor.

The open-circuit voltage of the STBY* pin is the input

3. When the regulator output is disabled the current drawn from

the input source is typically reduced to 4mA.

Figure 1

Turn-On Time:

voltage signal at pin 3 and enables the PT6980 series

regulation voltage. The total power-up time is less than

40ms, and is relatively independent of load, temperature,

and output capacitance. Figure 2 shows waveforms of the

waveforms were measured with a 12V input voltage, and

outputs respectively.

Figure 2

C

1

+

C

2

+

Inhibit

V

in

Vo

2

COM

COM

Q1

BSS138

Vo

1

C

3

+

4, 5, 6

PT6984

18–21

23

7–11

V

IN

Vo

2

GND

V

V

1

16

V

12–15

Vo

1

V

22

STBY

3

V1 (1V/Div)

V2 (1V/Div)

HORIZ SCALE: 5ms/Div

Vstby (10V/Div)