AD5231 datasheet(12/20 Pages) AD

12 / 20 page

REV. 0

–12–

AD5232

Table VI. Nominal Individual Segment Resistor Values ( )

Segment Resistor Size

for RAB End-to-End Values

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

AB) of

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:

RWB(Dx) = (Dx)/2

× R

BA + RW

(1)

Where

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

the RDACx latch, and RBA is the nominal end-to-end resistance.

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

RAB = 10 k

D (DEC)

RWB (V)

Output State

255

10011

Full-Scale

128

5050

Midscale

189

1 LSB

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

256

128

192

RWB

RWA

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

resistance RWA. Figure 10 shows the symmetrical programmabil-

ity of the various terminal connections. When these terminals

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

resistance value for RWA starts at a maximum value of resistance

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

value. The general transfer equation for this operation is:

RWA(Dx) = (2

N-Dx)/2N

× R

BA + RW

(2)

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

the RDACx latch, and RBA is the nominal end-to-end resistance.

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

Codes for RAB = 10 k

D (DEC)

RWA (W)

Output State

255

Full-Scale

128

5050

Midscale

10011

1 LSB

10050

Zero-Scale

The multichannel AD5232 has a

±0.2% typical distribution of

internal channel-to-channel RBA match. Device-to-device

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

variation. The change in RBA with temperature has a 600 ppm/

°C

temperature coefficient.

Device

Resolution

AD5231 数据表(PDF) 12 Page - Analog Devices

AD5231 数据表(HTML) 12 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

数据表下载