Application Notes

For technical support and more information, see inside back cover or visit www.ti.com/powertrends

PT6500 Series

Using the Standby Function on the

PT6500 5V/3.3V Bus Converters

For applications requiring output voltage On/Off control,

the 14-pin PT6500 ISR series incorporates a standby

function. This function may be used in applications that

require power-up/shutdown sequencing, and wherever

there is a requirement for the output status of the module

to be controlled by external circuitry.

The standby function is provided by the STBY* control,

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

normally, and provides a regulated output when a valid

supply voltage is applied to V

applied to pin-3 the regulator output will be disabled and

the input current drawn by the ISR will drop to less than

the regulator output during the period that input power is

applied.

The standby control pin is ideally controlled using an

open-collector (or open-drain) discrete transistor (See

Figure 1). It may also be driven directly from a dedicated

threshold requirements.

Parameter

Min

Max

Enable (VIH)

1V

5V

Disable (VIL)

–0.1V

0.35V

Notes:

1. The Standby/Inhibit control logic is similar for all Power

Trends’ modules, but the flexibility and threshold

tolerances will be different. For specific information on

this function for other regulator models, consult the

applicable application note.

2. The Standby control pin is ideally controlled using an

open-collector (or open-drain) discrete transistor and

requires no external pull-up resistor. The control input has

an open-circuit voltage of about 1Vdc. To disable the

regulator output, the control pin must be pulled to less

than 0.35Vdc with a low-level 0.5mA sink to ground.

3. The Standby input on the PT6500 series may be driven by

a differential output device, making it compatible with

TTL logic. A standard TTL logic gate will meet the

Do not use devices that can drive the Standby control input

above 5Vdc.

4. When the regulator output is disabled the current drawn

from the input source is reduced to approximately 30–

40mA (50mA maximum).

Figure 1

Turn-On Time:

In the circuit of Figure 1, turning Q

low voltage to the Standby control (pin 3) and disables the

regulator ouput. Correspondingly, turning Q

low-voltage signal and enables the output. The PT6500 ISR

series regulators have a fast response and will provide a fully

regulated output voltage within 250

µsec. The actual turn-on

time will vary with load and the total amount of output capaci-

tance. The waveform of Figure 2 shows the typical output

voltage response of a PT6501 (3.3V) following the turn-off of

Q

5Vdc input voltage, and 0.6

Ω load.

Figure 2

C

in

+

C

out

+

Inhibit

V

in

V

o

COM

COM

PT6500

11,12,13

14

7,8,9,10

4,5,6

Vin

V o

G N D

Vo(adj)

STBY

3

Vo(sense)

1

Q1

BSS138

+5V V

in

-50

0

50

100

150

200

250

300

350

t (

µµµµs )