REV. 0

AD5232

–7–

OPERATIONAL OVERVIEW

The AD5232 digital potentiometer is designed to operate as a

true variable resistor replacement device for analog signals that

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.

Table I. Set Two Digital POTs to Independent Data Values

then Save Wiper Positions in Corresponding Nonvolatile

EEMEM Registers

SDI

SDO

Action

Wiper W1 moves to 1/4 full-scale position.

Saves copy of RDAC1 register contents

into corresponding EEMEM0 register.

Wiper W2 moves to 1/2 full-scale position.

Saves copy of RDAC2 register contents

into corresponding EEMEM1 register.

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,

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

Ω to 10 kΩ optimizes the power

and switching speed trade-off.