Application Notes

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PT4400 Series

Using the Remote On/Off Function on the PT4400

Series of Isolated DC/DC Converters

For applications requiring output voltage On/Off control,

the PT4400 DC/DC converter series incorporates a “Re-

mote On/Off” control (pin 1). This feature can be used to

switch the module off without removing the applied

input source voltage.

The converter functions normally with Pin 1 open-circuit,

providing a regulated output voltage when a valid source

applied to pin 1, the converter output will be turned off.

Figure 1 is an application schematic, which shows the

typical use of the Remote On/Off function. Note the dis-

own internal pull-up, allowing it to be controlled with an

open-collector or open-drain device (See notes 2 & 3).

Table 1 gives the threshold requirements.

When placed in the “Off” state, the standby current drawn

from the input source is typically reduced to less than 1mA.

Parameter

Min

Typ

Max

Enable (VIH)

4.5V

—

—

Disable (VIL)

—

—

0.8V

Vo/c [Open-Circuit]

5.0V

Iin [pin 1 at –Vin]

—

—

–0.5mA

Notes:

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

transistor) for the Remote On/Off input. A pull-up

resistor is not necessary. To disable the output voltage,

the control pin should be pulled low to less than +0.8V.

3. The Remote On/Off pin may be controlled with devices that

have a totem-pole output. This is provided the output

If a TTL gate is used, a pull-up resistor may be required to

the logic supply voltage.

4. The PT4400 converters incorporate an “Under-Voltage

Lockout” (UVLO). The UVLO keeps the converter

off until the input voltage is close to the minimum

specified operating voltage. This is regardless of the

state of the Remote On/Off control. Table 2 gives the

UVLO input voltage thresholds.

Figure 1

Turn-On Time:

applies a low-voltage to pin 1 and disables the converter

be pulled high by an internal pull-up resistor. The con-

verter produces a regulated output voltage within 50ms.

Figure 2 shows the output response of a PT4401 following

voltage is short (<5ms), the indicated delay time will

vary depending upon the input voltage and the module’s

internal timing. The output voltage of the PT4401 was

set to 3.3V by connecting VID0 (pin 7), VID2 (pin 9),

and VID3 (pin 10) to the (–)Remote Sense (pin 12). The

waveforms were measured with 48VDC input voltage,

and a 10A resistive load.

Figure 2

L

O

A

D

PT4401

+V

sns

+V

out

-V

out

-V

sns

21

17–20

13–16

12

711

810

9

VID0 - VID4

+V

in

–V

in

4, 5

2, 3

1

Remote

On/Off

PROGRAMMING PINS

+3.3V

+V

IN

–V

IN

0V

– REMOTE SENSE

+ REMOTE SENSE

C

o

R1

10k

Q1

BSS138

Vdd

1 =OFF

Note 1

U1a

Note 1

Note 1

Series

UVLO Threshold

PT4400

36 – 75V

32V ±2V

Vo (1V/Div)

Iin (1A/Div)

Q1 Vgs (10V/Div)

HORIZ SCALE: 5ms/Div

Delay Time