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Application Notes

PT7670 Series

Pin-Coded Output Voltage Adjustment of the

PT7670 Series of 30-A Switching Regulators

The PT7670 Excalibur™ family of converters use a pin

code to adjust the output voltage. This feature uses the

control inputs, VID0–VID4 (pins 1–6). When these pins

are left open-circuit, the ISR regulates at its default output

voltage. Each of the programming pins are internally

applies a weighted change to the output voltage. By

output voltage of these ISRs can be programmed in

incremental steps over their specified output voltage

range. The program codes and output voltages offered

by these ISRs are compatible with the Voltage ID

specifications used by popular microprocessors. See

Figure 4-1 for the connection schematic, and the

respective device data sheet for the programming code

information.

Notes:

1. The programming convention is as follows:-

Logic 0:Connect to pin 12; Sense(–).

Logic 1:Open circuit/open drain (See Note 2)

2. For optimal output voltage accuracy Sense(–) (pin 12)

should always be used as the logic ‘0’ reference. The

input/output ground (pins 13-19) can also be used if

pin 12 is connected to pin 13 external to the module.

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

programming pins.

Figure 4-1

4. 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

divider network. Discrete transistors such as the BSS138,

2N7002, or IRLML2402 are examples of appropriate

devices.

Active Voltage Programming:

Special precautions should be taken when making changes

to the output voltage progam code while the unit is

powered. This activity can induce current transients

through the device as a result of the electrolytic output

capacitors being either charged or discharged to the new

output voltage set-point. The transient current can be

minimized by making only incremental changes to the

binary code, i.e. one LSB at a time. A minimum of 100µs

settling time between each program state is also recom-

mended. Making non-incremental changes to VID3 or

VID4 is discouraged.

When active devices are used to program the output

voltage, their state should be asserted prior to the input

power being applied. One approach is to pull STBY (pin 5)

control to GND prior to power up. After the host board

has then asserted the program code, the ground signal

to pin 5 can be removed. This will allow the regulator to

intiate a clean soft-start power-up to the desired program

voltage. For more information on the use of the Standby

function, consult the related application note, “Using

the Standby Function on the PT7670 Series of 30-A

Switching Regulators.”

C

out

+

C

in

+

1 µH

(Optional)

V

IN

COM

STBY

L

O

A

D

Q

1

L

1

Sense(–)

V

OUT

Power GND

PT7671

43

1

26

20–25

12

513–19

7–11

V

OUT

V

IN

GND

SNS(+)

SNS(–)

STBY

VID4 - VID0

2

6