AD5113 datasheet(20/24 Pages) AD

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AD5111/AD5113/AD5115

Data Sheet

Rev. 0 | Page 20 of 24

Similar to the mechanical potentiometer, the resistance of

the RDAC between the W terminal and the A terminal also

produces a digitally controlled complementary resistance, RWA.

RWA starts at the maximum resistance value and decreases as the

data loaded into the latch increases. The general equations for

this operation are

AD5111:

Bottom scale (7)

−

128

)

(

From 0 to 127 (8)

Top scale (9)

AD5113:

Bottom scale (10)

−

)

(

From 0 to 63 (11)

Top scale (12)

AD5115:

Bottom scale (13)

−

)

(

From 0 to 31 (14)

Top scale (15)

where:

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

RDAC register; 128, 64, and 32 refer to top scale step.

RAB is the end-to-end resistance.

RW is the wiper resistance.

RTS is the wiper resistance at top scale.

Regardless of which setting the part is operating in, take care

to limit the current between A to B, W to A, and W to B, to

the maximum continuous current of ±6 mA (5 kΩ and 10 kΩ)

or ±1.5 mA (80 kΩ), or pulse current specified in Table 6.

Otherwise, degradation or possible destruction of the internal

switch contact can occur.

PROGRAMMING THE POTENTIOMETER DIVIDER

Voltage Output Operation

The digital potentiometer easily generates a voltage divider at

W-to-B and W-to-A that is proportional to the input voltage at

A-to-B, as shown in Figure 44. Unlike the polarity of VDD to

GND, which must be positive, current across A-to-B, W-to-A,

and W-to-B can be in either direction.

Figure 44. Potentiometer Mode Configuration

If ignoring the effect of the wiper resistance for simplicity,

connecting Terminal A to 5 V and Terminal B to ground

produces an output voltage at W to B ranging from 0 V to 5 V.

The general equation defining the output voltage at VW with

respect to ground for any valid input voltage applied to

Terminal A and Terminal B, is

)

(

)

(

)

(

(16)

where:

RWB(D) can be obtained from Equation 1 to Equation 6.

RAW(D) can be obtained from Equation 7 to Equation 14.

Operation of the digital potentiometer in the divider mode

results in a more accurate operation over temperature. Unlike

the rheostat mode, the output voltage is dependent mainly

on the ratio of the internal resistors, RWA and RWB, and not the

absolute values. Therefore, the temperature drift reduces to

5 ppm/°C.

TERMINAL VOLTAGE OPERATING RANGE

The AD5111/AD5113/AD5115 are designed with internal

ESD diodes for protection. These diodes also set the voltage

boundary of the terminal operating voltages. Positive signals

present on the A, B, or W terminals that exceed VDD are

clamped by the forward-biased diode. There is no polarity

constraint between VA, VW, and VB, but they cannot be higher

than VDD or lower than GND.

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