AD5232 Analog Devices, AD5232 Datasheet - Page 12

• Manufacturer Part Number: AD5232
• Description: 2-Channel/ 256-Position Digital Potentiometer
• Manufacturer: Analog Devices

Device
Resolution
8-Bit
PROGRAMMING THE VARIABLE RESISTOR
Rheostat Operation
The nominal resistances of the RDAC between terminals A and B
are available with values of 10 k , 50 k , and 100 k . The final
digits of the part number determine the nominal resistance value,
e.g., 10 k = 10; 100 k = 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:
Where N is the resolution of the VR, Dx is the data contained in
the RDACx latch, and R
For example, the following output resistance values will be set
for the following RDAC latch codes (applies to the 8-bit, 10 k
potentiometers):
Table VII. Nominal Resistance Value at Selected Codes for
R
D (DEC)
255
128
1
0
AD5232
Note that in the zero-scale condition a finite wiper resistance of 50
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.
Table VI. Nominal Individual Segment Resistor Values ( )
AB
= 10 k
R
10 k
78.10
R
10011
5050
89
50
WB
WB
(Dx) = (Dx)/2
(V)
Version 50 k
BA
Output State
Full-Scale
Midscale
1 LSB
Zero-Scale (Wiper Contact Resistance)
for R
is the nominal end-to-end resistance.
Segment Resistor Size
390.5
N
AB
End-to-End Values
R
BA
Version 100 k
+ R
W
781.0
is present. Care
Version
AB
) of
(1)
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 R
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 R
and decreases as the data loaded in the latch is increased in
value. The general transfer equation for this operation is:
where N is the resolution of the VR, Dx is the data contained in
the RDACx latch, and R
For example, the following output resistance values will be set
for the following RDAC latch codes (applies to 8-bit, 10 k
potentiometers).
The multichannel AD5232 has a 0.2% typical distribution of
internal channel-to-channel R
matching is process-lot-dependent and exhibits a –40% to +20%
variation. The change in R
temperature coefficient.
Table VIII. Nominal Resistance Value at Selected
Codes for R
100
75
50
25
0
0
D (DEC)
255
128
1
0
WA
R
. Figure 10 shows the symmetrical programmabil-
WA
(Dx) = (2
AB
R
WB
= 10 k
WA
64
starts at a maximum value of resistance
R
89
5050
10011
10050
BA
BA
WA
is the nominal end-to-end resistance.
N
with temperature has a 600 ppm/ C
-Dx)/2
CODE – Decimal
(W)
BA
128
match. Device-to-device
N
Output State
Full-Scale
Midscale
1 LSB
Zero-Scale
R
BA
+ R
192
W
R
WA
256
(2)