Application Notes

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Using the Remote On/Off Function on the PT4500/

PT4520 Series of Isolated DC/DC Converters

For applications requiring output voltage on/off control,

the PT4500/4520 series of DC/DC converters incorporate

a remote on/off function. This function may be used in

applications that require battery conservation, power-up/

shutdown sequencing, and/or to coordinate the power-up

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

the related application note, SLTA021).

This function is provided by the Remote On/Off control,

pin1. If pin 1 is left open-circuit, the converter provides

Connecting pin 1 to pin 2, or applying a low-level signal

Table 3-1 provides details of the interface requirements

for the Remote On/Off pin. Figure 3-1 shows how a discrete

voltage rail and used with this control input.

Parameter

Min

Max

2.5V

–0.3V

0.8V

Notes:

side of the converter, as its ground reference. All

2. The on/off control internal circuitry is a high

impedance 10µA current source. The open-circuit

voltage may be as high as 8.3Vdc.

3. The PT4500/20 series incorporates an “Under-Voltage

Lockout” (UVLO) function. The UVLO prevents

operation of the converter when there is sufficient input

voltage to support a regulated output. Below the UVLO

threshold voltage, there is no output from the module

and the Remote On/Off control is inoperative.

4. The Remote On/Off input of the PT4500/20 series

must be controlled with a low-leakage (<100nA) open-

drain MOSFET.

5. When the converter output is disabled, the current

drawn from the input supply is typically reduced to

8mA (16mA maximum).

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 during power-up.

Figure 3-1

Turn-On Time:

The converter typically produces a fully

regulated output voltage within 35ms after the removal

of the low voltage signal from the Remote On/Off pin.

Using the circuit of Figure 3-1, Figure 3-2 shows the

output voltage and input current waveforms of a PT4521

sured with a 48Vdc input voltage, and 2.75-A resistive

load.

Figure 3-2

+V

in

– V

in

+V

o

– V

o

Q1

BSS138

V

GS

Note 4

PT4500/4520

+ Vout

–Vout

+Vin

–Vin

Remote

On/Off

V

1

2, 3

4, 5

9,10

7, 8

6

PT4500/4520 Series

Vout (2V/Div)

Iin (0.2A/Div)

Q1 Vgs (10V/Div)

HORIZ. SCALE: 5ms/Div