AD5171

APPLICATIONS

PROGRAMMABLE VOLTAGE REFERENCE (DAC)

It is common to buffer the output of the digital potentiometer

serves the purpose of impedance conversion as well as

delivering higher current, which may be needed.

GND

1U1

5V

2

3

AD8601

5V

A

W

B

AD1582

ADR03

A1

AD5171

U2

Figure 40. Programmable Voltage Reference (DAC)

GAIN CONTROL COMPENSATION

The digital potentiometers are commonly used in gain controls

(Figure 41) or sensor transimpedance amplifier signal

conditioning applications. To avoid gain peaking or in worst-

case oscillation due to step response, a compensation capacitor

is needed. In general, C2 in the range of a few picofarads to no

more than a few tenths of a picofarad is adequate for the

compensation.

U1

C2

4.7pF

A

B

W

R2 100k

Ω

R1

47k

Ω

Figure 41. Typical Noninverting Gain Amplifier

PROGRAMMABLE VOLTAGE SOURCE WITH

BOOSTED OUTPUT

For applications that require high current adjustment, such as a

laser diode driver or tunable laser, a boosted voltage source can

be considered (Figure 42).

+V

W

SIGNAL

LD

A

B

U1

AD5171

U3 2N7002

AD8601

U2

–V

Figure 42. Programmable Booster Voltage Source

to be equal to the wiper voltage set by the digital potentiometer.

The load current is then delivered by the supply via the N-Ch

100 mA with a 5 V supply. For precision applications, a voltage

reference such as ADR421, ADR03, or ADR370 can be applied

at the A terminal of the digital potentiometer.

LEVEL SHIFTING FOR DIFFERENT VOLTAGE

OPERATION

When users need to interface a 2.5 V controller with AD5171, a

proper voltage level shift must be employed so that the digital

potentiometer can be read from or written to the controller;

Figure 43 shows one of the implementations. M1 and M2

should be low threshold N-Ch power MOSFETs, such as

FDV301N.

2.5V

CONTROLLER

2.7V–5.5V

AD5171

Rp

Rp

Rp

Rp

G

G

S

D

M1

S

D

M2

SDA1

SCL1

SDA2

SCL2

Figure 43. Level Shifting for Different Voltage Operation

RESISTANCE SCALING

The AD5171 offers 5 kΩ, 10 kΩ, 50 kΩ, and 100 kΩ nominal

resistances. For users who need to optimize the resolution with

an arbitrary full-range resistance, the following techniques can

be used. By paralleling a discrete resistor (Figure 44) a

proportion tely lower voltage appears at terminal A to B, which

is applicable to only the voltage divider mode.

This translates into a finer degree of precision because the step

size at terminal W will be smaller. The voltage can be found as

DD

AB

AB

W

V

D

R

R

R

R

R

D

V

×

×

+

=

64

2

||

3

)

2

||

(

)

(

(5)

R1

R2

B

A

R3

W

Figure 44. Lowering the Nominal Resistance

Rev. PrC | Page 17 of 20

Preliminary Technical Data