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Application Notes

Using Remote On/Off on Power Trends’

30W Isolated DC-DC Converter Series

Power Trends’ 30W isolated series of DC/DC converters

incorporate a Remote On/Off function. This function may

be used in applications for battery conservation, power-

up/shutdown sequencing, or to co-ordinate the power-up

of the regulator for active in-rush current control. (See

TI application reports, SLTA021, and SLUA250).

The Remote On/Off function is provided by pin 2. If

pin 2 is left open-circuit, the converter provides a regu-

for this input. Figure 1 shows how a discrete MOSFET

to control the Remote On/Off pin.

Parameter

min

max

15V

–0.3V

0.8V

Notes:

1. These converters incorporate an “Under Voltage Lockout”

(UVLO) function. This function automatically holds the

converter output in the “Off” state until there is sufficient

input voltage for the converter to produce a regulated

output. Table 2 gives the applicable UVLO thresholds.

Table 2 UVLO Thresholds

Series

UVLO Threshold

PT3320/4560

34 ± 2.0V

36 – 75V

PT3340/4580

16.5 ± 1.5V

18 – 60V

ground reference. All voltages specified are with respect to

3. When the converter output is disabled the current drawn

from the input supply is typically reduced to 8mA (16mA

maximum).

4. The internal circuitry comprises of a high impedance (3µA

-10µA) current source. The open-circuit voltage is less

than 10V.

5. The Remote On/Off pin is ideally controlled using devices

with an open-collector (or open-drain) output. A small

low-leakage MOSFET (<100nA) is recommended. A

pull-up resistor is not required, but may be necessary to

(see Table 1).

Figure 1

Turn-On Time:

When the Remote On/Off input is left

open-circuit, the output of the converter is automatically

input power pins. The converter typically rises to full

regulation within 30ms of the application of power (or

after the release of the Remote On/Off pin with input

power applied). The actual turn-on time will vary with

the input voltage, output load, and the total amount of

capacitance connected to the output. Using the circuit of

Figure 1, Figure 2 shows the typical output voltage and

with a 48Vdc input voltage, and 5-A resistive load.

Figure 2

PT3320/3340/4560/4580 Series

30W Isolated

18

4, 5, 6

7, 8, 9

+Vin

+ V o u t

-Vin

Vo(adj)

Remote

On/Off

2

Sns(+)

19

10 - 12

-Vout

14 - 17

Sns(-)

13

C

out

+

C

in

+

Q1

BSS138

+V

o

–V

o

+V

in

-V

in

OFF/ ON

C

1

0.01µF

R

6. Keep the on/off transition to less than 1ms. This prevents

erratic operation of the ISR, whereby the output voltage

may drift un-regulated between 0V and the rated output

voltage during power-up.

susceptibility.

Vo (2V/Div)

Iin (0.5A/Div)

Q1Vgs (10V/Div)

HORIZ SCALE: 2ms/Div