AD5231 datasheet(10/24 Pages) AD

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AD5231

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OPERATIONAL OVERVIEW

The AD5231 digital potentiometer is designed to operate as a

true variable resistor replacement device for analog signals that

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 RDAC

ter allowing as many value changes as necessary to place the

potentiometer wiper in the correct position. The scratch pad

standard SPI serial interface mode by loading the complete repre-

sentative data word. Once a desirable position is found this value

can be saved into an 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.

There are 16 instructions that facilitate users’ programming

needs. Refer to Table III. The instructions are:

1. Do Nothing

2. Restore EEMEM Setting to RDAC

3. Save RDAC Setting to EEMEM

4. Save RDAC Setting or User Data to EEMEM

5. Decrement 6 dB

6. Decrement 6 dB

7. Decrement One Step

8. Decrement One Step

9. Reset EEMEM setting to RDAC

10. Read EEMEM to SDO

11. Read Wiper Setting to SDO

12. Write Data to RDAC

13. Increment 6 dB

14. Increment 6 dB

15. Increment One Step

16. Increment One Step

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

the wiper will be connected to the middle of the variable resistor.

And when the scratch pad is loaded with full-scale code, all ones,

the wiper will connect to the A-Terminal. Since the scratch pad

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 would load the

serial data input register with the command instruction #2,

which makes a copy of the desired wiper position data into the

nonvolatile EEMEM register. After 25 ms the wiper position

will be permanently stored in the nonvolatile EEMEM location.

Table I provides an application-programming example listing

the sequence of serial data input (SDI) words and the serial data

output appearing at the SDO Pin in hexadecimal format.

Table I. Set and Save RDAC Data to EEMEM Register

SDI

SDO

Action

B00100H

XXXXXXH

Loads data 100H into RDAC

full-scale position.

20XXXXH B00100H

Saves copy of RDAC register

contents into EEMEM register.

At system power ON, the scratch pad register is automatically

refreshed with the value last saved in the EEMEM register. The

factory preset EEMEM value is midscale but thereafter, the

EEMEM value can be changed by user.

CLK

SDI

IDD*

2mA/DIV

5V/DIV

* SUPPLY CURRENT RETURNS TO MINIMUM POWER CONSUMPTION

IF INSTRUCTION #0 (NOP) IS EXECUTED IMMEDIATELY AFTER

INSTRUCTION #1 (READ EEMEM)

4ms/DIV

TPC 19. IDD vs. Time (Read) Program Mode

CODE – Decimal

100

0.01

1024

0.1

RAB = 10k

RAB = 50k

RAB = 100k

896

768

640

512

384

128

256

VA = VB = OPEN

TA = 25 C

TPC 20. IWB_MAX vs. Code

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