AD5142ABCPZ10-RL7 datasheet(22/32 Pages) AD

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AD5122A/AD5142A

Data Sheet

Rev. A | Page 22 of 32

ADVANCED CONTROL MODES

The AD5122A/AD5142A digital potentiometers include a set

of user programming features to address the wide number of

applications for these universal adjustment devices (see Table 16

and Table 18).

Key programming features include the following:

•

Input register

•

Linear gain setting mode

•

A low wiper resistance feature

•

Linear increment and decrement instructions

•

±6 dB increment and decrement instructions

•

Burst mode

•

Reset

•

Shutdown mode

Input Register

The AD5122A/AD5142A include one input register per RDAC

associated RDAC register. These registers can be written to using

Command 2 and read back from using Command 3 (see Table 16).

This feature allows a synchronous update of one or both RDAC

registers at the same time.

The transfer from the input register to the RDAC register is

done synchronously by Command 8 (see Table 16).

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

automatically overwrites the associated input register.

Linear Gain Setting Mode

The patented architecture of the AD5122A/AD5142A allows

the independent control of each string resistor, RAW, and RWB. To

enable linear gain setting mode, use Command 16 (see Table 16)

to set Bit D2 of the control register (see Table 18).

This mode of operation can control the potentiometer as two

independent rheostats connected at a single point, W terminal,

as opposed to potentiometer mode where each resistor is

complementary, RAW = RAB − RWB.

This mode enables a second input and an RDAC register per

channel, as shown in Table 16; however, the actual RDAC

contents remain unchanged. The same operations are valid for

potentiometer and linear gain setting mode.

If the INDEP pin is pulled high, the device powers up in linear

gain setting mode and loads the values stored in the associated

memory locations for each channel (see Table 17). The INDEP pin

and the D2 bit are connected internally to a logic OR gate; if one or

both are set to 1, the parts cannot operate in potentiometer mode.

Low Wiper Resistance Feature

The AD5122A/AD5142A include two commands to reduce the

wiper resistance between the terminals when the device achieves

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

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

and bottom scale: by using Command 12 or Command 13

(see Table 16); by loading new data in an RDAC register, which

includes increment/decrement operations; or by entering

shutdown mode, Command 15 (see Table 16).

Table 12 and Table 13 show the truth tables for the top scale

position and the bottom scale position, respectively, when

potentiometer or linear gain setting mode is enabled.

Table 12. Top Scale Truth Table

Linear Gain Setting Mode

Potentiometer Mode

RAW

RWB

RAW

RWB

RAB

RTS

RAB

Table 13. Bottom Scale Truth Table

Linear Gain Setting Mode

Potentiometer Mode

RAW

RWB

RAW

RWB

RTS

RBS

RAB

RBS

Linear Increment and Decrement Instructions

The increment and decrement commands (Command 4 and

Command 5 in Table 16) 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 in multiple channels.

AD5142ABCPZ10-RL7 Datasheet(PDF) 22 Page - Analog Devices

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