AD5124 datasheet(27/36 Pages) AD

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Data Sheet

AD5124/AD5144/AD5144A

Rev. B | Page 27 of 36

ADVANCED CONTROL MODES

The AD5124/AD5144/AD5144A digital potentiometers include

a set of user programming features to address the wide number of

applications for these universal adjustment devices (see Table 20

and Table 22).

Key programming features include the following:

•

Input register

•

Linear gain setting mode

•

Low wiper resistance feature

•

Linear increment and decrement instructions

•

±6 dB increment and decrement instructions

•

Burst mode (I2C only)

•

Reset

•

Shutdown mode

Input Register

The AD5124/AD5144/AD5144A include one input register per

RDAC register. These registers allow preloading of the value for

the associated RDAC register. These registers can be written to

using Command 2 and read back from using Command 3 (see

Table 20).

This feature allows a synchronous and asynchronous update of

one or all of the RDAC registers at the same time.

The transfer from the input register to the RDAC register is

done asynchronously by the LRDAC pin or synchronously by

Command 8 (see Table 20).

If new data is loaded into an RDAC register, this RDAC register

automatically overwrites the associated input register.

Linear Gain Setting Mode

The proprietary architecture of the AD5124/AD5144/AD5144A

allows the independent control of each string resistor, RAW, and

RWB. To enable this feature, use Command 16 (see Table 20) to set

Bit D2 of the control register (see Table 22).

This mode of operation can control the potentiometer as two

independent rheostats connected at a single point, the W terminal.

This feature enables a second input and an RDAC register per

channel, as shown in Table 21, but the actual RDAC contents remain

unchanged. The same operations are valid for potentiometer and

linear gain setting modes. The EEPROM commands affect the

RWB resistance only. The parts restores in potentiometer mode

after a reset or power-up.

Low Wiper Resistance Feature

The AD5124/AD5144/AD5144A include two commands to

reduce the wiper resistance between the terminals when the

devices achieve full scale or zero scale. These extra positions are

called bottom scale, BS, and top scale, TS. The resistance between

Terminal A and Terminal W at top scale is specified as RTS.

Similarly, the bottom scale resistance between Terminal B and

Terminal W is specified as RBS.

The contents of the RDAC registers are unchanged by entering

into these positions. There are three ways to exit from top scale

and bottom scale: by using Command 12 or Command 13

(see Table 20); by loading new data in an RDAC register, which

includes increment/decrement operations; or by entering

shutdown mode, Command 15 (see Table 20).

Table 16 and Table 17 show the truth tables for the top scale

position and the bottom scale position, respectively, when the

potentiometer or linear gain setting mode is enabled.

Table 16. Top Scale Truth Table

Linear Gain Setting Mode

Potentiometer Mode

Table 17. Bottom Scale Truth Table

Linear Gain Setting Mode

Potentiometer Mode

Linear Increment and Decrement Instructions

The increment and decrement commands (Command 4 and

Command 5 in Table 20) are useful for linear step adjustment

applications. These commands simplify microcontroller software

coding by allowing the controller to send an increment or

decrement command to the device. The adjustment can be

individual or in a ganged potentiometer arrangement, where

all wiper positions are changed at the same time.

For an increment command, executing Command 4 automatically

moves the wiper to the next RDAC position. This command

can be executed in a single channel or multiple channels.

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