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Application Notes

PT4220/4240 Series

Using the Remote On/Off with the PT4220/4240

Isolated 10W Excalibur

 DC/DC Converters

For applications requiring output voltage On/Off control,

the PT4220/4240 DC/DC converter series incorporates

a “Remote 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

pin 1, the converter output will be turned off.

Figure 1 shows an application schematic, which details

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

discrete transistor (Q1). The pin has its 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 +0.8VDC.

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

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

voltage meets the threshold requirements in Table 1.

Do not apply more than +20V. If a TTL gate is used, a

pull-up resistor may be required to the logic supply voltage.

4. The PT4220/4240 converters incorporate an “Under-

Voltage Lockout” (UVLO). The UVLO will keep the

module off when the input voltage to the converter is

low, 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 60ms.

Figure 2 shows shows the output response of a PT4223

time of the output voltage is short (<5ms), the indicated

delay time will vary depending upon the input voltage

and the module’s internal timing. The waveform was

measured with a 48Vdc input voltage, and a 1.4A resis-

tive load.

Figure 2

R1

10k

Q1

BSS138

+V

o

-V

o

+V

in

-V

in

Vdd

1 =OFF

Note 1

U1a

Note 1

Note 1

PT4220/4240

+ V out

-Vout

+Vin

-Vin

Remote

On/Off

V

1

3

5

8, 9

6, 7

10

Series

UVLO Threshold

PT4220

36 – 75V

32V ±2V

PT4240

18 – 36V

15.8V ±2V

Vo (2V/Div)

Iin (0.2A/Div)

Q1Vgs (10V/Div)

HORIZ SCALE: 10ms/Div

Delay Time

Not Recommended For New Designs