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Application Notes

PT7710 Family

Pin-Coded Output Voltage Adjustment of the

PT7710 Excalibur™ Series of 20-A ISRs

The PT7710 Excalibur™ family of converters incorporate

a pin-coded control to adjust the output voltage. This

feature uses the control pins VID0–VID4 (pins 1–6).

When the control pins are left open-circuit, the ISR

output regulates at its default output voltage. Each

control pin is internally connected to a precision resistor,

which when grounded applies a weighted change to the

output voltage. By selectively grounding VID0–VID4,

the output voltage of these ISRs can be programmed in

incremental steps over the specified output voltage range.

The program codes and output voltage range offered by

these ISRs are compatible with the Voltage ID specifica-

tions defined by Intel Corporation for VRMs (voltage

regulator modules). The codes are used by both the

Pentium® and Athlon® microprocessors. Refer to

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 (Remote Sense Ground).

Logic 1:

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

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

programming pins.

3. Use pin 12 (Remote Sense Ground) as the logic “0”

reference. While the regular ground (pins 13-19) can also

be used for programming, doing so will degrade the load

reglation of the product. If the remote sense ground is

not used, pin 12 must be connected to pin 13 for

optimum output voltage accuracy.

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. An alternative is to pull pin 5 (STBY)

control to GND during the application of input voltage,

then assert the required program code and release pin 5.

The module will then intiate a soft-start power-up to the

desired program voltage. For more information on the

use of the Standby function, consult the related applica-

tion note, “Using the Standby Function on the PT7710

Excalibur™ Series of 20-A ISRs.”

C

out

+

C

in

+

1µH

(Optional)

+5V

COM

STBY

L

O

A

D

PT7710

64321

26

20-25

12

5

13-19

27

7-11

Vo

Vin

GND

SNS(+)

SNS(-)

Synch

Out

STBY

VID4 - VID0