AD5112 AD [Analog Devices], AD5112 Datasheet - Page 19

• Manufacturer Part Number: AD5112
• Manufacturer: AD [Analog Devices]

Data Sheet
RDAC ARCHITECTURE
To achieve optimum performance, Analog Devices, Inc., has
patented the RDAC segmentation architecture for all the digital
potentiometers. In particular, the
employ a two-stage segmentation approach as shown in
Figure 42. The
designed with the transmission gate CMOS topology and with
the gate voltage derived from V
Low Wiper Resistance Feature
In addition, the
feature to reduce the resistance between terminals. These extra
steps are called bottom scale and top scale. At bottom scale, the
typical wiper resistance decreases from 70 Ω to 45 Ω. At top
scale, the resistance between Terminal A and Terminal W is
decreased by 1 LSB and the total resistance is reduced to 70 Ω.
The extra steps are not equal to 1 LSB and are not included in
the INL, DNL, R-INL, and R-DNL specifications.
5-BIT/6-BIT/7-BIT
ADDRESS
DECODER
Figure 42.
AD5111/AD5113/AD5115
AD5111/AD5113/AD5115
AD5111/AD5113/AD5115
B
A
R
R
R
R
L
L
L
L
DD
AD5111/AD5113/AD5115
.
BS
TS
Simplified RDAC Circuit
wiper switch is
include a new
R
R
S
S
W
Rev. 0 | Page 19 of 24
PROGRAMMING THE VARIABLE RESISTOR
Rheostat Operation—±8% Resistor Tolerance
The
only two terminals are used as a variable resistor. The unused
terminal can be floating or tied to the W terminal as shown in
Figure 43.
The nominal resistance between Terminal A and Terminal B,
R
tap points accessed by the wiper terminal. The 5-/6-/7-bit data
in the RDAC latch is decoded to select one of the 128/64/32
possible wiper settings. The general equations for determining
the digitally programmed output resistance between the W
terminal and B terminal are
AD5111:
AD5113:
AD5115:
where:
D is the decimal equivalent of the binary code in the 5-/6-/7-bit
RDAC register; 128, 64, and 32 refer to the top scale step.
R
R
R
AB
AB
W
BS
, is available in 5 kΩ, 10 kΩ, and 80 kΩ and has 128/64/32
is the wiper resistance.
is the wiper resistance at bottom scale.
is the end-to-end resistance.
AD5111/AD5113/AD5115
R
R
R
R
R
R
WB
WB
WB
WB
WB
WB
A
B
(
(
(



D
D
D
R
R
R
)
)
)
BS

BS

BS

W
Figure 43. Rheostat Mode Configuration
128
64
32
D
D
D



R
R
R
AB
AB
AB


AD5111/AD5113/AD5115
A
B

R
R
R
W
W
W
W
operate in rheostat mode when
A
B
From 0 to 128 (2)
Bottom scale (1)
Bottom scale (3)
From 0 to 64 (4)
Bottom scale (5)
From 0 to 32 (6)
W