AD5171

Rev. D | Page 19 of 24

APPLICATIONS INFORMATION

DAC

It is common to buffer the output of the digital potentiometer as

impede conversion and deliver higher current, if needed.

GND

1

5V

2

3

AD8601

5V

A

W

B

U1

AD1582

A1

AD5171

U2

Figure 39. Programmable Voltage Reference (DAC)

GAIN CONTROL COMPENSATION

The digital potentiometers are commonly used in gain

controls or sensor transimpedance amplifier signal conditioning

applications (see Figure 40). 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 a

few tenths of a picofarad is adequate for the compensation.

U1

C2

4.7pF

A

B

W

R2 100kΩ

R1

47kΩ

Figure 40. 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 (see Figure 41).

+V

W

SIGNAL

LD

A

B

U1

AD5171

U3 2N7002

AD8601

U2

–V

Figure 41. 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 the ADR421, ADR03, or ADR370, can be

applied at Terminal A of the digital potentiometer.

LEVEL SHIFTING FOR DIFFERENT VOLTAGE

OPERATION

If the SCL and SDA signals come from a low voltage logic

level shift the signals for read/write communications between

the AD5171 and the controller. Figure 42 shows one of the

implementations. For example, when SDA1 is at 2.5 V, M1 turns

off, and SDA2 becomes 5 V. When SDA1 is at 0 V, M1 turns on,

and SDA2 approaches 0 V. As a result, proper level shifting is

established. 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 42. 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, a proportionately lower

voltage appears at Terminal A to Terminal B, which is applicable

only to the voltage divider mode (see Figure 43).

This translates into a finer degree of precision because the step

size at Terminal W is smaller. The voltage can be found as

DD

AB

AB

W

V

D

R2

R

R3

R2

R

D

V

×

×

+

=

64

||

)

||

(

)

(

(5)

R1

R2

B

A

R3

W

Figure 43. Lowering the Nominal Resistance