Application Notes

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Pin-Coded Output Voltage Adjustment of

PT7761 “Excalibur™” ISRs

The PT7761 Excalibur power module incorporates a

pin-coded output voltage control. These regulators in-

clude five control pins, identified VID0–VID4 (pins 1–5)

respectively. By selectively grounding VID0-VID4, the

output voltage of this regulator can be programmed in

incremental steps over the output voltage range, 1.3V to

3.5V. The program code and voltage range is designed to

be compatible with the “Voltage ID” specification defined

for popular microprocessors. Refer to Figure 1 for the

connection schematic, and the applicable data sheet for

the program code.

Notes:

1. The programming convention is as follows:-

Logic 0:

Connect to pin15 (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 15 (Rem Sense Gnd) as the logic “0” reference.

While the regular ground (pins 16–22) can also be used for

programming, doing so will degrade the load regulation of

the product. If the remote sense ground is not used,

pin 15 must be connected to pin 16 for optimum

output voltage accuracy.

Figure 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

voltage control circuit. Discrete transistors such as the

BSS138, 2N7002, IRLML2402, are examples of

appropriate devices.

Active Voltage Programming:

Special precautions should be taken when making changes

to the voltage control progam code while the unit is

powered. It is highly recommended that the ISR be either

powered down or held in standby. Changes made to the

transients through the device. This is the result of the

electrolytic output capacitors being either charged or dis-

charged 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 recommended. Making non-incremental

changes to VID3 and VID4 with the output enabled is

discouraged. If they are changed, the transients induced

can overstress the device. If the program code cannot be

asserted prior to power-up, pull pin 6 (STBY) to GND

during the period that the input voltage is applied. The

release of pin 6 will then to allow the device to initiate a

soft-start power-up to the program voltage.

PT7761

C

out

+

C

in

+

1

µH

(Optional)

+5V

COM

STBY

L

O

A

D

PT7761

432

1

3 1

23 – 30

15

61 6 – 22

9 – 14

5

7

S y n c

GND

Sns ( + )

Sns ( – )

V

OUT

V

IN

Stb y

VID0 - VID4