AD5232 Analog Devices, AD5232 Datasheet - Page 7

• Manufacturer Part Number: AD5232
• Description: 2-Channel/ 256-Position Digital Potentiometer
• Manufacturer: Analog Devices

OPERATIONAL OVERVIEW
The AD5232 digital potentiometer is designed to operate as a
true variable resistor replacement device for analog signals that
remain within the terminal voltage range of V
The basic voltage range is limited to a |V
digital potentiometer wiper position is determined by the RDAC
register contents. The RDAC register acts as a scratch pad,
register allowing as many value changes as necessary to place the
potentiometer wiper in the correct position. The scratch pad
register can be programmed with any position value using the
standard SPI serial interface mode by loading the complete
representative data word. Once a desirable position is found,
this value can be saved into a corresponding EEMEM register.
Thereafter the wiper position will always be set at that position
for any future ON-OFF-ON power supply sequence. The
EEMEM save process takes approximately 25 ms, during this
time the shift register is locked preventing any changes from
taking place. The RDY pin indicates the completion of this
EEMEM save.
SCRATCH PAD AND EEMEM PROGRAMMING
The scratch pad register (RDAC register) directly controls the
position of the digital potentiometer wiper. When the scratch
pad register is loaded with all zeros, the wiper will be connected
to the B-Terminal of the variable resistor. When the scratch pad
register is loaded with midscale code (1/2 of full-scale position),
the wiper will be connected to the middle of the variable resis-
tor. And when the scratch pad is loaded with full-scale code, all
1s, the wiper will connect to the A-Terminal. Since the scratch
pad register is a standard logic register, there is no restriction on
the number of changes allowed. The EEMEM registers have a
program erase/write cycle limitation described in the Flash/
EEMEM Reliability section.
BASIC OPERATION
The basic mode of setting the variable resistor wiper position
(programming the scratch pad register) is accomplished by
loading the serial data input register with the command instruc-
tion #11, which includes the desired wiper position data. When
the desired wiper position is found, the user loads the serial data
input register with the command instruction #2, which copies
the desired wiper position data into the corresponding nonvola-
tile EEMEM register. After 25 ms the wiper position will be
permanently stored in the corresponding nonvolatile EEMEM
location. Table I provides an application-programming example
listing the sequence of serial data input (SDI) words and the
corresponding serial data output appearing at the SDO pin in
hexadecimal format.
At system power-on, the scratch pad register is refreshed with
the value last saved in the EEMEM register. The factory preset
EEMEM value is midscale. The scratch pad (wiper) register can
be refreshed with the current contents of the nonvolatile
EEMEM register under hardware control by pulsing the PR pin.
DD
– V
SS
< V
SS
| < 5.5 V. The
TERM
< V
DD
.
Table I. Set Two Digital POTs to Independent Data Values
then Save Wiper Positions in Corresponding Nonvolatile
EEMEM Registers
SDI
B040
20xx
B180
21xx
Be aware that the PR pulse first sets the wiper at midscale when
brought to logic zero, and then on the positive transition to logic
high, it reloads the DAC wiper register with the contents of
EEMEM. Many additional advanced programming commands
are available to simplify the variable resistor adjustment process.
For example, the wiper position can be changed one step at a
time by using the software-controlled Increment/Decrement
instruction or, by 6 dB at a time, with the Shift Left/Right
instruction command. Once an Increment, Decrement, or Shift
command has been loaded into the shift register, subsequent CS
strobes will repeat this command. This is useful for push-button
control applications. See the Advanced Control Modes descrip-
tion following Table I. A serial data output SDO pin is
available for daisy chaining and for readout of the internal
register contents. The serial input data register uses a 16-bit
[instruction/address/data] WORD.
EEMEM PROTECTION
Write protect (WP) disables any changes of the scratch pad
register contents regardless of the software commands, except
that the EEMEM setting can be refreshed using commands 8
and PR. Therefore, the write-protect (WP) pin provides a hard-
ware EEMEM protection feature. Execute a NOP command
before returning WP to logic high.
DIGITAL INPUT/OUTPUT CONFIGURATION
All digital inputs are ESD-protected high input impedance that
can be driven directly from most digital sources. PR and WP,
which are active at logic low, must be biased to V
not being used. No internal pull-up resistors are present on any
digital input pins.
The SDO and RDY pins are open-drain digital outputs where
pull-up resistors are needed only if using these functions. A
resistor value in the range of 1 k to 10 k optimizes the power
and switching speed trade-off.
H
H
H
H
SDO
XXXX
B040
20xx
B180
H
H
H
H
Action
Loads 40
Wiper W1 moves to 1/4 full-scale position.
Saves copy of RDAC1 register contents
into corresponding EEMEM0 register.
Loads 80
Wiper W2 moves to 1/2 full-scale position.
Saves copy of RDAC2 register contents
into corresponding EEMEM1 register.
H
H
data into RDAC1 register,
data into RDAC2 register,
AD5232
DD
if they are