AD5122 datasheet(24/32 Pages) AD

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AD5122/AD5142

Data Sheet

Rev. 0 | Page 24 of 32

±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 16).

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 14).

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 AD5122/AD5142 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 14. 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

Reset

The AD5122/AD5142 can be reset through software by executing

Command 14 (see Table 16) or through hardware on the low pulse

of the RESET pin. 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. Tie RESET to VLOGIC if

the RESET pin is not used.

Shutdown Mode

The AD5122/AD5142 can be placed in shutdown mode by

executing the software shutdown command, Command 15 (see

Table 16); and by setting the LSB (D0) to 1. This feature places

the RDAC in a special state. The contents of the RDAC register are

unchanged by entering shutdown mode. However, all commands

listed in Table 16 are supported while in shutdown mode. Execute

Command 15 (see Table 16) and set the LSB (D0) to 0 to exit

shutdown mode.

Table 15. Truth Table for Shutdown Mode

Linear Gain Setting Mode

Potentiometer Mode

N/A1

Open

N/A1

1 N/A = not applicable.

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 18), which protects the

EEPROM and RDAC registers independently.

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

the EEPROM into the RDAC register.

INDEP PIN

If the INDEP pin is pulled high at power-up, the part operates

in linear gain setting mode, loading each string resistor, RAWx and

RWBx, with the value stored into the EEPROM (see Table 17). If

the pin is pulled low, the part powers up in potentiometer mode.

The INDEP pin and the D2 bit are connected internally to a logic

OR gate, if any or both are 1, the part cannot operate in

potentiometer mode (see Table 18).

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