EVAL-AD5262EBZ Analog Devices Inc, EVAL-AD5262EBZ Datasheet - Page 17

• Manufacturer Part Number: EVAL-AD5262EBZ
• Description: EVALUATION BOARD
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD5262EBZ

• Main Purpose: Digital Potentiometer
• Utilized Ic / Part: AD5262
• Primary Attributes: Dual Channel, 256 Positions
• Secondary Attributes: SPI Interface
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Embedded: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

accessed by the wiper terminal, plus the B terminal contact. The
8-bit data in the RDAC latch is decoded to select one of the 256
possible settings. Assuming a 20 kΩ part is used, the wiper’s first
connection starts at the B terminal for data 0x00. Because there
is a 60 Ω wiper contact resistance, such a connection yields a
minimum of 60 Ω resistance between Terminal W and Terminal B.
The second connection is the first tap point corresponding to
138 Ω (R
connection is the next tap point representing 216 Ω (78 × 2 + 60)
for Data 0x02, and so on. Each LSB data value increase moves
the wiper up the resistor ladder until the last tap point is reached at
19,982 Ω (R
to the B terminal. See Figure 53 for a simplified diagram of the
equivalent RDAC circuit.
The general equation determining the digitally programmed
output resistance between W and B is
where D is the decimal equivalent of the binary code that is
loaded in the 8-bit RDAC register and R
to-end resistance.
For example, when R
open circuit, the following output resistance values of R
set for the RDAC latch codes shown in Table 9. The result is the
same if Terminal A is tied to W.
Table 9. R
RDAC (Dec)
256
128
1
0
Note that in the zero-scale condition, a finite wiper resistance of
60 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 switches.
Like the mechanical potentiometer the RDAC replaces, the
AD5260/AD5262 are completely symmetrical. The resistance
between Wiper W and Terminal A also produces a digitally
controlled complementary resistance, R
symmetrical programmability of the various terminal connec-
tions. When R
tied to the wiper. Setting the resistance value for R
maximum value of resistance and decreases as the data loaded
in the latch is increased in value. The general equation for this
operation is
For example, when R
open circuit, the following output resistance values of R
R
R
WB
WA
WB
(
(
D
WB
D
= R
AB
)
)
vs. Code
− 1 LSB + R
=
=
WA
AB
R
19,982
10,060
138
60
256
256
/256 R
D
WB
is used, the B terminal can be left floating or
256
(Ω)
×
−
AB
AB
R
D
W
AB
= 20 kΩ, V
= 20 kΩ, V
×
= 78 Ω + 60 Ω) for Data 0x01. The third
W
R
+
Output State
Full scale (R
Midscale
1 LSB
Zero-scale (wiper contact resistance)
). The wiper does not directly connect
AB
R
W
+
R
W
B
A
= 0 V, and the A terminal is
= 0 V, and the B terminal is
AB
– 1 LSB + R
WA
AB
. Figure 54 shows the
is the nominal end-
WA
W
)
starts at a
WB
WA
are
are
Rev. A | Page 17 of 24
(1)
(2)
set for the RDAC latch codes shown in Table 10. The result is
the same if Terminal B is tied to Terminal W.
Table 10. R
RDAC (Dec)
256
128
1
0
The typical distribution of the nominal resistance R
channel to channel matches within ±1%. Device-to-device
matching is process lot-dependent with the worst case of
±30% variation. However, because the resistance element
is processed in thin film technology, the change in R
temperature has a low 35 ppm/°C temperature coefficient.
PROGRAMMING THE POTENTIOMETER DIVIDER
Voltage Output Operation
The digital potentiometer easily generates output voltages at
wiper-to-B and wiper-to-A to be proportional to the input
voltage at A-to-B. Ignore the effect of the wiper resistance. For
example, connecting the A terminal to 5 V and the B terminal
to ground produces an output voltage at W-to-B starting at 0 V
up to 1 LSB less than 5 V. Each LSB of voltage is equal to the
voltage applied across Terminal A and Terminal B divided by
the 256 positions of the potentiometer divider. Because the
AD5260/AD5262 operate from dual supplies, the general
equation defining the output voltage at V
ground for any given input voltage applied to Terminal A and
Terminal B is
Operation of the digital potentiometer in the divider mode
results in more accurate operation over temperature. Unlike the
rheostat mode, the output voltage is dependent on the ratio of
the internal resistors, R
therefore, the drift reduces to 5 ppm/°C.
V
20
16
12
W
8
4
0
(
0
D
Figure 54. AD5260/AD5262 Equivalent RDAC Circuit
)
WA
=
vs. Code
256
R
D
WA
×
R
60
10,060
19,982
20,060
64
V
WA
AB
WA
(Ω)
+
and R
V
CODE (Decimal)
B
WB
128
, and not the absolute values;
R
AB
Output State
Full scale
Half scale
1 LSB
Zero scale
AD5260/AD5262
= 20kΩ
W
with respect to
192
R
WB
AB
AB
from
with
256
(3)