AD5116 datasheet(24/28 Pages) AD

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AD5110/AD5112/AD5114

Data Sheet

Rev. 0 | Page 24 of 28

RDAC ARCHITECTURE

To achieve optimum performance, Analog Devices, Inc., has

patented the RDAC segmentation architecture for all the digital

potentiometers. In particular, the AD5110/AD5112/AD5114

employ a two-stage segmentation approach as shown in

Figure 46. The AD5110/AD5112/AD5114 wiper switch is

designed with the transmission gate CMOS topology and with

the gate voltage derived from VDD.

6-BIT/7-BIT/8-BIT

ADDRESS

DECODER

Figure 46. AD5110/AD5112/AD5114 Simplified RDAC Circuit

Top Scale/Bottom Scale Architecture

In addition, the AD5110/AD5112/AD5114 include a new

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.

PROGRAMMING THE VARIABLE RESISTOR

Rheostat Operation—±8% Resistor Tolerance

The AD5110/AD5112/AD5114 operate in rheostat mode when

only two terminals are used as a variable resistor. The unused

terminal can be floating or tied to the Terminal W as shown in

Figure 47.

Figure 47. Rheostat Mode Configuration

The nominal resistance between Terminal A and Terminal B,

RAB, is available in 5 kΩ, 10 kΩ, and 80 kΩ and has 32/64/128

tap points accessed by the wiper terminal. The 5-/6-/7-bit data

in the RDAC latch is decoded to select one of the 32/64/128

possible wiper settings. The general equations for determining

the digitally programmed output resistance between the W

terminal and B terminal are

AD5110:



Bottom scale (0xFF) (1)







128

)

(

From 0x00 to 0x80 (2)

AD5112:



Bottom scale (0xFF) (3)







)

(

From 0x00 to 0x40 (4)

AD5114:



Bottom scale (0xFF) (5)







)

(

From 0x00 to 0x20 (6)

where:

D is the decimal equivalent of the binary code in the 5-/6-/7-bit

RDAC register.

RAB is the end-to-end resistance.

RW is the wiper resistance.

RBS is the wiper resistance at bottom scale

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