EVAL-AD5142DBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
EVAL-AD5142DBZ
Analog Devices
'EVAL-AD5142DBZ' PDF : 32 Pages View PDF
Data Sheet
AD5122/AD5142
RDAC ARCHITECTURE
To achieve optimum performance, Analog Devices, Inc., uses a
proprietary RDAC segmentation architecture for all the digital
potentiometers. In particular, the AD5122/AD5142 employ a
three stage segmentation approach, as shown in Figure 42. The
AD5122/AD5142 wiper switch is designed with the transmission
gate CMOS topology and with the gate voltage derived from
VDD and VSS.
A
STS
The nominal resistance between Terminal A and Terminal B, RAB,
is 10 kΩ or 100 kΩ, and has 128/256 tap points accessed by the
wiper terminal. The 7-bit/8-bit data in the RDAC latch is decoded
to select one of the 128/256 possible wiper settings. The general
equations for determining the digitally programmed output
resistance between Terminal W and Terminal B are
AD5122:
RWB
(D)
D
128
RAB
RW
From 0x00 to 0x7F (1)
RH
RH
RM
RM
RL
AD5142:
RWB
(D)
D
256
RAB
RW
From 0x00 to 0xFF (2)
where:
D is the decimal equivalent of the binary code in the 7-bit/8-bit
RDAC register.
RAB is the end-to-end resistance.
W
RW is the wiper resistance.
7-BIT/8-BIT
ADDRESS
DECODER
RL
RM
RH
RM
RH
SBS
In potentiometer mode, similar to the mechanical potentiometer,
the resistance between Terminal W and Terminal A also produces
a digitally controlled complementary resistance, RWA. RWA also
gives a maximum of 8% absolute resistance error. RWA starts at the
maximum resistance value and decreases as the data loaded into
the latch increases. The general equations for this operation are
AD5122:
B
RAW
(D)
128 D
128
RAB
RW
From 0x00 to 0x7F (3)
Figure 42. AD5122/AD5142 Simplified RDAC Circuit
Top Scale/Bottom Scale Architecture
In addition, the AD5122/AD5142 include new positions to
reduce the resistance between terminals. These positions are
called bottom scale and top scale. At bottom scale, the typical
wiper resistance decreases from 130 Ω to 60 Ω (RAB = 100 kΩ).
At top scale, the resistance between Terminal A and Terminal W is
decreased by 1 LSB, and the total resistance is reduced to 60 Ω
(RAB = 100 kΩ).
PROGRAMMING THE VARIABLE RESISTOR
Rheostat Operation—±8% Resistor Tolerance
The AD5122/AD5142 operate in rheostat mode when only two
terminals are used as a variable resistor. The unused terminal can
be floating, or it can be tied to Terminal W, as shown in Figure 43.
A
W
A
W
A
W
B
B
B
Figure 43. Rheostat Mode Configuration
AD5142:
RAW
(D)
256
256
D
RAB
RW
From 0x00 to 0xFF (4)
where:
D is the decimal equivalent of the binary code in the 7-bit/8-bit
RDAC register.
RAB is the end-to-end resistance.
RW is the wiper resistance.
If the device is configured in linear gain setting mode, the
resistance between Terminal W and Terminal A is directly
proportional to the code loaded in the associate RDAC register.
The general equations for this operation are
AD5122:
R AW
(D)
D
128
R AB
RW
From 0x00 to 0x7F (5)
AD5142:
R AW
(D)
D
256
R AB
RW
From 0x00 to 0xFF (6)
where:
D is the decimal equivalent of the binary code in the 7-bit/8-bit
RDAC register.
RAB is the end-to-end resistance.
RW is the wiper resistance.
Rev. C | Page 27 of 32
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