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MAX5440
(Rev.:2006)

Stereo Volume Control with Rotary Encoder Interface

Maxim Integrated 

Stereo Volume Control

with Rotary Encoder Interface

Detailed Description

The MAX5440 dual, 40kΩ logarithmic taper digital

potentiometer features a debounced up/down interface

for use with a simple rotary encoder without using a

microcontroller. Each potentiometer has 32 log-spaced

tap points with a buffered wiper output and replaces

mechanical potentiometers.

Mode Control (MODE)

The MAX5440 MODE input toggles between volume

and balance modes. Force MODE low to toggle

between volume and balance modes. For example, dri-

ving MODE low once while in volume-control mode

switches the MAX5440 to balance mode. Driving MODE

low again switches the MAX5440 back to volume mode.

MODE is internally pulled high with a 45kΩ resistor to

VLOGIC. The MAX5440 powers up in volume-control

mode. Leave unconnected or connect to VLOGIC if bal-

ance mode is not required.

Rotary Encoder Interface

The MAX5440 interfaces with rotary encoder switches.

The rotary encoder is a contact closure type switch with

two outputs that connect to RENCODEA and

RENCODEB on the device. As the shaft is rotated,

RENCODEA and RENCODEB produce a gray code

count. Figure 1 shows a typical rotary encoder interface.

State changes trigger a wiper movement and the direc-

tion of the count dictates the direction of wiper move-

ment. An increasing gray code count moves the wiper

up to a lower attenuation setting in volume mode and

towards a full right channel (CH1) in balance mode. A

decreasing gray code count moves the wiper down to a

higher attenuation in volume mode and towards a full left

channel (CH0) in balance mode. Both switch inputs are

internally pulled up to VLOGIC by internal 45kΩ resistors.

During rapid rotation, the inputs must be stable for at

least 20ms and have separation between state

changes by at least 40ms for the debounce circuitry to

accurately detect the input states.

ROTARY

ENCODER

VLOGIC

1/4 CYCLE PER DETENT

CW

CHANNEL A

45kΩ

45kΩ

RENCODEA

A

RENCODEB

B

MAX5440

GND

OPEN CIRCUIT

CLOSED CIRCUIT

OPEN CIRCUIT

CLOSED CIRCUIT

DD D D DDD DDD DD DD D DD

CHANNEL B

CLOCKWISE ROTATION

INCREASING GRAY CODE (AB)

11, 10, 00, 01, 11, 10, ETC.

COUNTERCLOCKWISE ROTATION

DECREASING GRAY CODE (AB)

11, 01, 00, 10, 11, 01, ETC.

Figure 1. Rotary Encoder Interface

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