Nonvolatile Memory, Dual
1024-Position Digital Potentiometer
Data Sheet
Rev. F
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FEATURES
Dual-channel, 1024-position resolution
25 k, 250 k nominal resistance
Maximum ±8% nominal resistor tolerance error
Low temperature coefficient: 35 ppm/°C
2.7 V to 5 V single supply or ±2.5 V dual supply
SPI-compatible serial interface
Nonvolatile memory stores wiper settings
Power-on refreshed with EEMEM settings
Permanent memory write protection
Resistance tolerance stored in EEMEM
26 bytes extra nonvolatile memory for user-defined
information
1M programming cycles
100-year typical data retention
APPLICATIONS
DWDM laser diode driver, optical supervisory systems
Mechanical potentiometer replacement
Instrumentation: gain, offset adjustment
Programmable voltage-to-current conversion
Programmable filters, delays, time constants
Programmable power supply
Low resolution DAC replacement
Sensor calibration
GENERAL DESCRIPTION
The AD5235 is a dual-channel, nonvolatile memor
y,1 digitally
controlled potentiomet
er2 with 1024-step resolution, offering
guaranteed maximum low resistor tolerance error of ±8%.
The device performs the same electronic adjustment function
as a mechanical potentiometer with enhanced resolution, solid
state reliability, and superior low temperature coefficient per-
formance. The versatile programming of the AD5235 via an
SPI-compatible serial interface allows 16 modes of operation
and adjustment including scratchpad programming, memory
storing and restoring, increment/decrement, ±6 dB/step log taper
adjustment, wiper setting readback, and extra EEMEM1 for user-
defined information such as memory data for other components,
look-up table, or system identification information.
FUNCTIONAL BLOCK DIAGRAM
ADDR
DECODE
AD5235
RDAC1
SERIAL
INTERFACE
CS
CLK
SDI
SDO
PR
WP
RDY
RDAC1
REGISTER
EEMEM1
RDAC2
REGISTER
EEMEM2
26 BYTES
RTOL*
USER EEMEM
POWER-ON
RESET
W1
B1
RDAC2
W2
B2
A1
VDD
A2
VSS
GND
02816-
001
EEMEM
CONTROL
*RAB TOLERANCE
Figure 1.
In the scratchpad programming mode, a specific setting can
be programmed directly to the RDAC2 register, which sets the
resistance between Terminal W and Terminal A and Terminal W
and Terminal B. This setting can be stored into the EEMEM
and is restored automatically to the RDAC register during
system power-on.
The EEMEM content can be restored dynamically or through
external PR strobing, and a WP function protects EEMEM
contents. To simplify the programming, the independent or
simultaneous linear-step increment or decrement commands
can be used to move the RDAC wiper up or down, one step at
a time. For logarithmic ±6 dB changes in the wiper setting, the
left or right bit shift command can be used to double or halve the
RDAC wiper setting.
The AD5235 patterned resistance tolerance is stored in the
EEMEM. The actual end-to-end resistance can, therefore, be
known by the host processor in readback mode. The host can
execute the appropriate resistance step through a software
routine that simplifies open-loop applications as well as
precision calibration and tolerance matching applications.
The AD5235 is available in a thin, 16-lead TSSOP package.
The part is guaranteed to operate over the extended industrial
temperature range of 40°C to +85°C.
1
The terms nonvolatile memory and EEMEM are used interchangeably.
2
The terms digital potentiometer and RDAC are used interchangeably.