Dual, 64-Position Nonvolatile Digital

Potentiometer with Buffered Outputs

6

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POT0

H0

V0

L0

H1

V1

L1

INTERFACE

SDA

SCL

A0

A1

A2

WP

GND

DS3908

PGA0

POT1

PGA1

1x, 2x, 4x GAIN

F8h

F9h

FAh

FBh

G1

G0

EEPROM

1x, 2x, 4x GAIN

POT0 REGISTER

POT1 REGISTER

POT0/1 REGISTER

Functional Diagram

Detailed Description

The DS3908 contains two nonvolatile digital poten-

tiometers with programmable-gain amplifiers buffering

the wiper outputs.

The potentiometers have 63 equally weighted (linear-

taper) resistive elements, for a total of 64 taps. The

resistive elements are built using a low-temperature-

drift material, and have a typical 100k

Ω end-to-end

resistance. This produces an output that is highly lin-

ear, with the highest and lowest taps connected to high

(Hx) and low (Lx) terminals, respectively. The poten-

compatible interface. Three address pins allow one of

eight slave addresses to be selected. The eight slave

addresses allow the DS3908 address to be customized

The potentiometer positions are saved in EEPROM, and

are recalled during each power-up to provide non-

volatile position settings. Once the settings are written,

the write-protect pin prevents accidental writes to the

potentiometers. The write-protection function is ideal for

analog factory calibration because it prevents errant

of the device. The WP pin contains an internal pullup

resistor that must be pulled low to write to the device.

The programmable-gain amplifiers can be indepen-

dently set to one of three different gains—1V/V, 2V/V, or

4V/V. The amplifiers’ common-mode input range is from

and capable of driving 1mA loads, 300mV from each

supply rail. The outputs are stable driving 100pF loads

for applications that require output filtering.

The addition of the amplifier to buffer the potentiometer

wiper offers distinct advantages over standard digital

potentiometers. The buffer provides a high-impedance

load for the potentiometer and a low-impedance volt-

age output. This improves the linearity of the output

voltage for systems that load the potentiometer by elim-

inating the changes in current through both the poten-

tiometer and the wiper impedance. It also allows

voltage gain from the potentiometer input to the output.

Because the amplifiers are integrated into the DS3908,

this is done without increasing the footprint of the

design or the complexity of the PC board.