Datasheet

Data Sheet AD5124/AD5144/AD5144A
Rev. A | 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 (I
2
C 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 patented architecture of the AD5124/AD5144/AD5144A
allows the independent control of each string resistor, R
AW
, and
R
WB
. 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
R
WB
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 R
TS
.
Similarly, the bottom scale resistance between Terminal B and
Terminal W is specified as R
BS
.
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
R
AW
R
WB
R
AW
R
WB
R
AB
R
AB
R
TS
R
AB
Table 17. Bottom Scale Truth Table
Linear Gain Setting Mode Potentiometer Mode
R
AW
R
WB
R
AW
R
WB
R
TS
R
BS
R
AB
R
BS
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.