AD5232
Data Sheet
THEORY OF OPERATION
The AD5232 digital potentiometer is designed to operate as a
true variable resistor replacement device for analog signals that
The application programming example shown in Table 6 lists
two digital potentiometers set to independent data values. The
wiper positions are then saved in the corresponding nonvolatile
EEMEMx registers.
remain within the terminal voltage range of VSS < VTERM < VDD
.
The basic voltage range is limited to a |VDD − VSS| < 5.5 V. The
digital potentiometer wiper position is determined by the RDACx
register contents. The RDACx register acts as a scratch pad register,
allowing as many value changes as necessary to place the poten-
tiometer 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. When a desirable position is found, this value can be
saved into a corresponding EEMEMx register. Thereafter, the wiper
position is always set at that position for any future on-off-on
power supply sequence. The EEMEM save process takes approx-
imately 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.
Table 6. Application Programming Example
SDI
SDO
Action
0xB040
0xXXXX1 Loads 0x40 data into the RDAC1 register;
Wiper W1 moves to 1/4 full-scale position.
0x20XX1 0xB040
Saves a copy of the RDAC1 register contents
into the corresponding EEMEM1 register.
0xB180
0x20XX1 Loads 0x80 data into the RDAC2 register;
Wiper W2 moves to 1/2 full-scale position.
0x21XX1 0xB180
Saves a copy of the RDAC2 register contents
into the corresponding EEMEM2 register.
1 X = don’t care.
PR
Note that the
pulse first sets the wiper at midscale when it is
brought to Logic 0. Then, on the positive transition to logic high,
it reloads the DAC wiper register with the contents of EEMEMx.
Many additional advanced programming commands are avail-
able to simplify the variable resistor adjustment process.
SCRATCH PAD AND EEMEM PROGRAMMING
The scratch pad register (RDACx register) directly controls the
position of the digital potentiometer wiper. When the scratch
pad register is loaded with all 0s, the wiper is connected to
Terminal B of the variable resistor. When the scratch pad register
is loaded with midscale code (1/2 of full-scale position), the wiper
is connected to the middle of the variable resistor. When the
scratch pad is loaded with full-scale code, which is all 1s, the
wiper connects to Terminal A. Because the scratch pad register
is a standard logic register, there is no restriction on the number
of changes allowed. The EEMEMx registers have a program
erase/write cycle limitation that is described in the Flash/EEMEM
Reliability section.
For example, the wiper position can be changed, one step at
a time, by using the software controlled increment/decrement
command instructions. The wiper position can be also be changed,
6 dB at a time, by using the shift left/right command instructions.
After an increment, decrement, or shift command instruction is
CS
loaded into the shift register, subsequent
strobes repeat this
command instruction. This is useful for push-button control appli-
cations (see the Advanced Control Modes section). The 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.
BASIC OPERATION
The basic mode of setting the variable resistor wiper position
(by programming the scratch pad register) is accomplished by
loading the serial data input register with 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 Command Instruction 2, which copies
the desired wiper position data into the corresponding non-
volatile EEMEMx register. After 25 ms, the wiper position is
permanently stored in the corresponding nonvolatile EEMEM
location. Table 6 provides an application programming example
listing the sequence of serial data input (SDI) words and the
corresponding serial data output appearing at the serial data
output (SDO) pin in hexadecimal format.
EEMEM PROTECTION
WP
The write protect ( ) pin disables any changes of the scratch
pad register contents, regardless of the software commands,
except that the EEMEM setting can be refreshed using Instruction
PR
WP
Command 8 and . Therefore, the
pin provides a hardware
EEMEM protection feature. Execute an NOP command (Com-
WP
mand Instruction 0) before returning
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. The
pins, which are active at logic low, must be biased to VDD if they
are not being used. No internal pull-up resistors are present on
any digital input pins.
PR
WP
and
At system power-on, the scratch pad register is refreshed with
the last value saved in the EEMEMx register. The factory preset
EEMEM value is midscale. The scratch pad (wiper) register can
be refreshed with the current contents of the nonvolatile EEMEMx
The SDO and RDY pins are open-drain, digital outputs when pull-
up resistors are needed, but only if these functions are in use.
A resistor value in the range of 1 kΩ to 10 kΩ optimizes the power
and switching speed trade-off.
PR
register under hardware control by pulsing the
pin.
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