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Application Notes

PT4400 Series

Pin-Coded Output Voltage Adjustment on the

PT4400 Programmable DC/DC Converters

The PT4400 series of isloated DC/DC converters have

a programmable output voltage. In each case the desired

output voltage must be selected from one of a number of

discrete voltages using the voltage programming control

pins. Depending on each model’s resolution and adjust-

ment range, there are up to five control pins. They are

identified VID0–VID4 (pins 7–11) respectively. By

selectively strapping these control pins to (–)Remote

Sense (pin 12), the output voltage can be programmed

in incremental steps over the defined output voltage range.

The program code and output voltage range of the PT4401

is also compatible with the “Voltage ID” code defined in

the Intel® VRM 8.2 specification. Refer to Figure 1 for

the connection schematic, and the product specification

sheet for each model’s applicable program code.

Notes:

1. The programming convention is as follows:-

Logic 0:

Connect to pin 12 (–Remote Sense).

Logic 1:

Open circuit/open drain (See notes 2, & 4)

2. Do not connect pull-up resistors to the voltage

programming pins.

3. To minimize output voltage error, always use pin 12

(-Remote Sense) as the logic “0” reference. While -Vout

(pins 13-16) can also be used for programming, doing so

will degrade the voltage selection accuracy and load

regulation of the product.

4. When VID0–VID4 are all open circuit (logic 1), the

output voltage is undefined. In this state the output

voltage of the converter cannot be guaranteed, and can

vary with output load and input voltage.

Figure 1

5. On all models other than the PT4401, the contol input

VID4 (pin 11) is internally disabled and not functional.

6. If active devices are used to ground the voltage control

pins, low-level open drain MOSFET devices should be

bipolar devices introduces errors in the device’s internal

voltage control circuit. Discrete transistors such as the

BSS138 or IRLML2402 are examples of appropriate

devices.

Active Voltage Programming:

Special precautions should be taken when making changes

to the voltage progam code while the output is active.

This activity induces a transient, which may activate

the module’s output over-voltage (OV) protection. Once

triggered the OV protection circuit latches the output

off, and requires the momentary removal of input power

to reset the module. OV protection trips can be avoided

by limiting the output voltage adjustment to no more

than a 15% change from the initial voltage. Large transi-

tions are best made with a series of incremental changes,

allowing 100µs settling time between each program state.

When using active devices to program the output voltage,

their state should be asserted prior to input power being

applied. An alternative is to pull pin 1 (Remote On/Off)

the required program code, and then release pin 1. The

module will than initiate a soft-start power-up to the

desired program voltage.

L

O

A

D

PT4400

+V

sns

+V

out

-V

out

-V

sns

21

17 – 20

13 – 16

12

71 1

81 0

9

VID0 - VID4

+V

in

– V

in

4, 5

2, 3

1

Remote

On/Off

PROGRAMMING PINS

+V

OUT

+V

IN

– V

IN

– REMOTE SENSE

+ REMOTE SENSE

C

o

Q1

BSS138

INH

– V

OUT