AD5231 datasheet(16/24 Pages) AD

16 / 24 page

REV. 0

AD5231

–16–

()

–

=×

1024

(2)

For example, the following output resistance values will be set

for the following RDAC latch codes with VDD = 5 V (applies to

RAB = 10 k

Ω Digital Potentiometers):

Table VIII. RWA(D) at Selected Codes for RAB = 10 k

Ω

D(DEC)

RWA(D) (

Ω)

Output State

1023

24.7

Full-Scale

512

5015

MidScale

10005

1 LSB

10015

Zero-Scale

The typical distribution of RAB from device-to device matches tightly

when they are processed at the same batch. When devices are pro-

cessed at different time, device-to device matching becomes process

lot dependent and exhibits a –40% to +20% variation. The change

in RAB with temperature has a 600 ppm/

°C temperature coefficient.

PROGRAMMING THE POTENTIOMETER DIVIDER

Voltage Output Operation

The digital potentiometer can be configured to generate an

output voltage at the wiper terminal which is proportional to the

input voltages applied to terminals A and B. For example con-

necting A-terminal to 5 V and B-terminal to ground produces

an output voltage at the wiper which can be any value starting at

0 V up to 5 V. Each LSB of voltage is equal to the voltage applied

across terminal AB divided by the 2

N position resolution of the

potentiometer divider.

Since AD5231 can also be supplied by dual supplies, the general

equation defining the output voltage at VW with respect to ground

for any given input voltages applied to terminals A and B is:

WAB

()

=×

1024

(3)

Equation 3 assumes VW is buffered so that the effect of wiper

resistance is nulled. Operation of the digital potentiometer in the

divider mode results in more accurate operation over temperature.

Here the output voltage is dependent on the ratio of the internal

resistors and not the absolute value, therefore, the drift improves

to 15 ppm/

°C. There is no voltage polarity restriction between

terminals A, B, and W as long as the terminal voltage (VTERM)

stays within VSS < VTERM < VDD.

PROGRAMMING EXAMPLES

The following programming examples illustrate typical sequence of

events for various features of the AD5231. Users should refer to

Table III for the instructions and data word format. The Instruction

numbers, addresses, and data appearing at SDI and SDO Pins are

based in hexadecimal in the following examples.

Table IX. Scratch Pad Programming

SDI

SDO

Action

B00100H

XXXXXXH

Loads data 100H into RDAC

full-scale position.

Table X. Incrementing RDAC Followed by Storing the Wiper

Setting to EEMEM

SDI

SDO

Action

B00100H

XXXXXXH

Loads data 100H into RDAC

full-scale position.

E0XXXXH B00100H

Increments RDAC register by one

to 101H.

E0XXXXH E0XXXXH

Increments RDAC register by one

to 102H.

Continue until desired wiper position is reached.

20XXXXH XXXXXXH

Saves RDAC register data into

EEMEM.

Optionally tie

WP to GND to protect EEMEM values.

Table XI. Restoring EEMEM Value to RDAC Register

EEMEM value for RDAC can be restored by Power On, or

Strobing

PR pin, or Programming shown below.

SDI

SDO

Action

10XXXXH XXXXXXH

Restores EEMEM value to RDAC

00XXXXH 10XXXXH

NOP. Recommended step to

minimize power consumption.

8XXXXXH 00XXXXH

Reset EEMEM value to RDAC

Table XII. Using Left Shift by One to Increment +6 dB Step

SDI

SDO

Action

C0XXXXH XXXXXXH

Moves wiper to double the present

data contained in RDAC register.

Table XIII. Storing Additional User Data in EEMEM

SDI

SDO

Action

32AAAAH

XXXXXXH

Stores data AAAAH into spare

EEMEM location USER1. (Allowable

to address in 14 locations with

maximum 16 bits of Data.)

335555H

32AAAAH

Stores data 5555H into spare EEMEM

location USER2.

(Allowable to address in 14 locations

with maximum 16 bits of Data.)

Table XIV. Reading Back Data From Various Memory Locations

SDI

SDO

Action

92XXXXH XXXXXXH

Prepares data read from USER1

location.

00XXXXH 92AAAAH

NOP instruction #0 sends 24-bit

word out of SDO where the last 16

bits contain the contents of USER1

location. NOP command ensures

device returns to idle power dissi-

pation state.

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