Datasheet

AD5200/AD5201
–12–
D7
D6
D5
D4
D3
D2
D1
D0
RDAC
LATCH &
DECODER
SHDN
SW
SHDN
SW
2
N
1
SW
2
N
2
SW
1
SW
0
A
R
R
R
B
W
DIGITAL CIRCUITRY
OMITTED FOR CLARITY
R
R
AB
2
N
–1
Figure 2a. AD5200 Equivalent RDAC Circuit. 255 positions
can be achieved up to Switch SW
2
N
–1
.
SW
2
N
1
D5
D4
D3
D2
D1
D0
RDAC
LATCH &
DECODER
SW
2
N
2
SW
1
SW
0
R
R
R
R
B
W
DIGITAL CIRCUITRY
OMITTED FOR CLARITY
SHDN
A
SW
SHDN
SW
2
N
R
R
AB
2
N
Figure 2b. AD5201 Equivalent RDAC Circuit. Unlike AD5200,
33 positions can be achieved all the way to Switch SW
2
N
.
The general equation determining the digitally programmed
output resistance between W and B is:
RD
D
R
WB AB
()
=+
255
50 Ω
for AD5200 (1)
RD
D
R
WB AB
()
=+
32
50 Ω
for AD5201 (2)
where:
D is the decimal equivalent of the data contained in
RDAC latch.
R
AB
is the nominal end-to-end resistance.
R
W
is the wiper resistance contributed by the on-resistance
of the internal switch.
Note D in AD5200 is between 0 to 255 for 256 positions. On
the other hand, D in AD5201 is between 0 to 32 so that 33
positions can be achieved due to the slight internal structure
difference, Figure 2b.
Again if R
AB
= 10 kΩ and A terminal can be opened or tied to
W, the following output resistance between W to B will be set
for the following RDAC latch codes:
AD5200 Wiper-to-B Resistance
DR
WB
(DEC) () Output State
255 10050 Full-Scale (R
AB
+ R
W
)
128 5070 Midscale
189 1 LSB
0 50 Zero-Scale (Wiper Contact Resistance)
AD5201 Wiper-to-B Resistance
DR
WB
(DEC) () Output State
32 10050 Full-Scale (R
AB
+ R
W
)
16 5050 Midscale
1 363 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 no more than ±20 mA to avoid
degradation or possible destruction of the internal switch contact.
Like the mechanical potentiometer the RDAC replaces, it is
totally symmetrical. The resistance between the wiper W and
Terminal A also produces a digitally controlled resistance R
WA
.
When these terminals are used, the B terminal should be tied to
the wiper. Setting the resistance value for R
WA
starts at a maxi-
mum value of resistance and decreases as the data loaded in
the latch is increased in value. The general equation for this
operation is:
RD
D
R
WA AB
()
=
−
()
+
255
255
50 Ω
for AD5200 (3)
RD
D
R
WA AB
()
=
−
()
+
32
32
50 Ω
for AD5201 (4)
Similarly, D in AD5200 is between 0 to 255, whereas D in
AD5201 is between 0 to 32.
For R
AB
= 10 kΩ and B terminal is opened or tied to the wiper
W, the following output resistance between W and A will be set
for the following RDAC latch codes: