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AD5123/AD5143

Data Sheet

Rev. B | Page 22 of 28

±6 dB Increment and Decrement Instructions

Two programming instructions produce logarithmic taper

increment or decrement of the wiper position control by

an individual potentiometer or by a ganged potentiometer

arrangement where all RDAC register positions are changed

simultaneously. The +6 dB increment is activated by Command 6,

and the −6 dB decrement is activated by Command 7 (see Table 15).

For example, starting with the zero-scale position and executing

Command 6 ten times moves the wiper in 6 dB steps to the full-

scale position. When the wiper position is near the maximum

setting, the last 6 dB increment instruction causes the wiper to

go to the full-scale position (see Table 13).

Incrementing the wiper position by +6 dB essentially doubles

the RDAC register value, whereas decrementing the wiper

position by −6 dB halves the register value. Internally, the

AD5123/AD5143 use shift registers to shift the bits left and

right to achieve a ±6 dB increment or decrement. These

functions are useful for various audio/video level adjustments,

especially for white LED brightness settings in which human

visual responses are more sensitive to large adjustments than to

small adjustments.

Table 13. Detailed Left Shift and Right Shift Functions for

the ±6 dB Step Increment and Decrement

Left Shift (+6 dB/Step)

Right Shift (−6 dB/Step)

0000 0000

1111 1111

0000 0001

0111 1111

0000 0010

0011 1111

0000 0100

0001 1111

0000 1000

0000 1111

0001 0000

0000 0111

0010 0000

0000 0011

0100 0000

0000 0001

1000 0000

0000 0000

1111 1111

0000 0000

Burst Mode

By enabling the burst mode, multiple data bytes can be sent to

the device consecutively. After the command byte, the device

interprets the consecutive bytes as data bytes for the command.

A new command can be sent by generating a repeat start or by a

stop and start condition.

The burst mode is activated by setting Bit D3 of the control

Reset

The AD5123/AD5143 can be reset through software by executing

Command 14 (see Table 15). The reset command loads the

RDAC registers with the contents of the EEPROM and takes

approximately 30 µs. The EEPROM is preloaded to midscale at

the factory, and initial power-up is, accordingly, at midscale.

Shutdown Mode

The AD5123/AD5143 can be placed in shutdown mode by

executing the software shutdown command, Command 15

(see Table 15), and setting the LSB (D0) to 1. This feature places

the RDAC in a zero power consumption state where the device

operates in potentiometer mode, Terminal A is open-circuited,

and the wiper, Terminal W, is connected to Terminal B; however, a

finite wiper resistance of 40 Ω is present. When the device is

configured in linear gain setting mode, the resistor addressed,

RAW or RWB, is internally place at high impedance. Table 14

shows the truth table depending on the device operating mode.

The contents of the RDAC register are unchanged by entering

shutdown mode. However, all commands listed in Table 15 are

supported while in shutdown mode. Execute Command 15 (see

Table 15) and set the LSB (D0) to 0 to exit shutdown mode.

Table 14. Truth Table for Shutdown Mode

Linear Gain Setting Mode

Potentiometer Mode

RAW

RWB

RAW

RWB

High impedance

RBS

EEPROM OR RDAC REGISTER PROTECTION

The EEPROM and RDAC registers can be protected by disabling

any update to these registers. This can be done by using software or

by using hardware. If these registers are protected by software,

set Bit D0 and/or Bit D1 (see Table 17), which protects the RDAC

and EEPROM registers independently.

When RDAC is protected, the only operation allowed is to copy

the EEPROM into the RDAC register.

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