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AD5232

Data Sheet

Rev. C | Page 20 of 24

PROGRAMMING THE POTENTIOMETER DIVIDER

Voltage Output Operation

The digital potentiometer easily generates an output voltage pro-

portional to the input voltage applied to a given terminal. For

example, connecting Terminal A to 5 V and Terminal B to GND

produces an output voltage at the wiper that can be any value

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

applied across Terminal A to Terminal B, divided by the 2N

position resolution of the potentiometer divider. The general

equation defining the output voltage with respect to ground for

any given input voltage applied to Terminal A to Terminal B is

)

(

)

(

)

(

(3)

where RWB(D) can be obtained from Equation 1 and RWA(D)

can be obtained from Equation 2.

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,

not the absolute value; therefore, the drift improves to 15 ppm/°C.

There is no voltage polarity restriction between Terminal A,

Terminal B, and Wiper Terminal W as long as the terminal voltage

(VTERM) stays within VSS < VTERM < VDD.

OPERATION FROM DUAL SUPPLIES

The AD5232 can be operated from dual supplies, enabling

control of ground-referenced ac signals (see Figure 42 for

a typical circuit connection).

AD5232

VSS

GND

SDI

CLK

SCLK

MOSI

GND

VDD

±2V p-p

±1V p-p

VDD

+2.5V

–2.5V

MicroConverter

Figure 42. Operation from Dual Supplies

The internal parasitic capacitances and the external capacitive

loads dominate the ac characteristics of the RDACs. When

configured as a potentiometer divider, the −3 dB bandwidth of

the AD5232BRU10 (10 kΩ resistor) measures 500 kHz at half

scale. Figure 14 provides the large signal BODE plot character-

istics of the three resistor versions: 10 kΩ, 50 kΩ, and 100 kΩ (see

Figure 43 for a parasitic simulation model of the RDAC circuit).

RDAC

10kΩ

45pF

60pF

Figure 43. RDAC Circuit Simulation Model for RDACx = 10 kΩ

The following code provides a macro model net list for the

10 kΩ RDAC:

.PARAM DW=255, RDAC=10E3

.SUBCKT DPOT (A,W,B)

CA A 0 {45E-12}

RAW A W {(1-DW/256)*RDAC+50}

CW W 0 60E-12

RBW W B {DW/256*RDAC+50}

CB B 0 {45E-12}

.ENDS DPOT

APPLICATION PROGRAMMING EXAMPLES

The command sequence examples shown in Table 14 to Table 18

have been developed to illustrate a typical sequence of events

for the various features of the AD5232 nonvolatile digital poten-

tiometer. Table 14 illustrates setting two digital potentiometers

to independent data values.

Table 14.

SDI

SDO

Action

0xB140

0xXXXX

Loads 0x40 data into the RDAC2 register;

Wiper W2 moves to 1/4 full-scale position.

0xB080

0xB140

Loads 0x80 data into the RDAC1 register;

Wiper W1 moves to 1/2 full-scale position.

Table 15 illustrates the active trimming of one potentiometer,

followed by a save to nonvolatile memory (PCB calibrate).

Table 15.

SDI

SDO

Action

0xB040

0xXXXX

Loads 0x40 data into the RDAC1 register;

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

0xE0XX

0xB040

Increments the RDAC1 register by 1, to 0x41;

Wiper W1 moves one resistor segment

away from Terminal B.

0xE0XX

Increments the RDAC1 register by 1, to 0x42;

Wiper W1 moves one more resistor segment

away from Terminal B. Continue until

desired the wiper position is reached.

0x20XX

0xE0XX

Saves the RDAC1 register data into the

corresponding nonvolatile EEMEM1

memory: ADDR = 0x0.

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