REV. 0

–12–

AD5232

Table VI. Nominal Individual Segment Resistor Values ( )

Segment Resistor Size

10 k

Version 50 k

Version 100 k

Version

8-Bit

78.10

390.5

781.0

PROGRAMMING THE VARIABLE RESISTOR

Rheostat Operation

The nominal resistances of the RDAC between terminals A and B

are available with values of 10 k

Ω, 50 kΩ, and 100 kΩ. The final

digits of the part number determine the nominal resistance value,

e.g., 10 k

Ω = 10; 100 kΩ = 100. The nominal resistance (R

the AD5232 VR has 256 contact points accessed by the wiper

terminal, plus the B terminal contact. The 8-bit data word in the

RDAC latch is decoded to select one of the 256 possible settings.

The general transfer equation, which determines the digitally

programmed output resistance between Wx and Bx, is:

N

× R

(1)

Where

N is the resolution of the VR, Dx is the data contained in

For example, the following output resistance values will be set

for the following RDAC latch codes (applies to the 8-bit, 10 k

Ω

potentiometers):

Table VII. Nominal Resistance Value at Selected Codes for

D (DEC)

Output State

255

10011

Full-Scale

128

5050

Midscale

189

1 LSB

0

50

Zero-Scale

*(Wiper Contact Resistance)

*Note that in the zero-scale condition a finite wiper resistance of 50

Ω is present. Care

should be taken to limit the current flow between W and B in this state to a

maximum continuous value of 2 mA to avoid degradation or possible de struc-

tion of the internal switch metalization. Intermittent current operation to

20 mA is allowed.

CODE – Decimal

100

75

0

0

256

64

128

192

50

25

Figure 10. Symmetrical RDAC Operation

Like the mechanical potentiometer the RDAC replaces, the

AD5232 parts are totally symmetrical. The resistance between

the wiper W and terminal A also produces a digitally controlled

ity of the various terminal connections. When these terminals

are used the B–terminal should be tied to the wiper. Setting the

and decreases as the data loaded in the latch is increased in

value. The general transfer equation for this operation is:

× R

(2)

where N is the resolution of the VR, Dx is the data contained in

For example, the following output resistance values will be set

for the following RDAC latch codes (applies to 8-bit, 10 k

Ω

potentiometers).

Table VIII. Nominal Resistance Value at Selected

D (DEC)

Output State

255

89

Full-Scale

128

5050

Midscale

1

10011

1 LSB

0

10050

Zero-Scale

The multichannel AD5232 has a

±0.2% typical distribution of

matching is process-lot-dependent and exhibits a –40% to +20%

°C

temperature coefficient.

Device

Resolution