AD5262 datasheet(16/20 Pages) AD

16 / 20 page

REV. 0

–16–

AD5260/AD5262

that can deliver 20 mA at 2.048 V. The load current is simply the

voltage across terminals B-to-W of the digital pot divided by RS.

REF

(7)

–5V

VOUT

OP1177

–

+5V

100

102

B W

AD5260

1 F

GND

REF191

SLEEP

VIN

2U1

0 TO (2.048

VL)

–2.048V TO VL

Figure 19. Programmable 4-to-20 mA Current Source

The circuit is simple, but be aware that dual-supply op amps are

ideal because the ground potential of REF191 can swing from

–2.048 V at zero scale to VL at full scale of the potentiometer

setting. Although the circuit works under single supply, the pro-

grammable resolution of the system will be reduced.

Programmable Bidirectional Current Source

For applications that require bidirectional current control or higher

voltage compliance, a Howland current pump can be a solution

(see Figure 20). If the resistors are matched, the load current is:

R B R

()

(8)

–5V

+5V

AD8016

–15V

+15V

–15V

OP2177

AD5260

10pF

150k

10pF

15k

R2A

14.95k

500

+15V

Figure 20. Programmable Bidirectional Current Source

Programmable Low-Pass Filter

Digital potentiometer AD5262 can be used to construct a second

order Sallen Key Low-Pass Filter (see Figure 21). The design

equations are:

(9)

RR C C

12 12

(10)

R C

(11)

Users can first select some convenient values for the capacitors.

To achieve maximally flat bandwidth where Q = 0.707, let C1 be

twice the size of C2 and let R1 = R2. As a result, users can adjust

R1 and R2 to the same settings to achieve the desirable bandwidth.

AD8601

+2.5V

–2.5V

ADJUSTED TO

SAME SETTINGS

Figure 21. Sallen Key Low-Pass Filter

Programmable Oscillator

In a classic Wien-bridge oscillator, Figure 22, the Wien network

(R, R

’, C, C’) provides positive feedback, while R1 and R2

provide negative feedback. At the resonant frequency, fo, the

overall phase shift is zero, and the positive feedback causes the

circuit to oscillate. With R = R

’, C = C’, and R2 = R2A//(R2B+

RDIODE), the oscillation frequency is:

(12)

where R is equal to RWA such that:

256

–

(13)

At resonance, setting

(14)

balances the bridge. In practice, R2/R1 should be set slightly larger

than 2 to ensure the oscillation can start. On the other hand, the

alternate turn-on of the diodes D1 and D2 ensures R2/R1 to be

smaller than 2 momentarily and therefore stabilizes the oscillation.

Once the frequency is set, the oscillation amplitude can be tuned

by R2B since:

VI R B V

(15)

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