ADR440 datasheet(16/20 Pages) AD

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ADR440/ADR441/ADR443/ADR444/ADR445

Rev. E | Page 16 of 20

Table 9. Digital Potentiometer Parts

Part No.

No. of

Channels

No. of

Positions

ITF

R (kΩ)

VDD1

(V)

AD5251

2.00

64.00

I2C

1, 10, 50, 100

5.5

AD5207

2.00

256.00

SPI

10, 50, 100

5.5

AD5242

2.00

256.00

I2C

10, 100, 1M

5.5

AD5262

2.00

256.00

SPI

20, 50, 200

AD5282

2.00

256.00

I2C

20, 50, 100

AD5252

2.00

256.00

I2C

1, 10, 50, 100

5.5

AD5232

2.00

256.00

SPI

10, 50, 100

5.5

AD5235

2.00

1024.00

SPI

25, 250

5.5

ADN2850

2.00

1024.00

SPI

25, 250

5.5

1 Can also use a negative supply.

Adding a negative supply to the operational amplifier allows

the user to produce a negative programmable reference

by connecting the reference output to the inverting terminal

of the operational amplifier. Choose feedback resistors to

minimize errors over temperature.

PROGRAMMABLE CURRENT SOURCE

It is possible to build a programmable current source using a

setup similar to the programmable voltage source, as shown in

Figure 38. The constant voltage on the gate of the transistor sets

the current through the load. Varying the voltage on the gate

changes the current. This circuit does not require a dual digital

potentiometer.

ADR440/

ADR441/

ADR443/

ADR444/

ADR445

VIN

VOUT

GND

ILOAD

VCC

RSENSE

AD5259

0.1µF

Figure 38. Programmable Current Source

HIGH VOLTAGE FLOATING CURRENT SOURCE

Use the circuit in Figure 39 to generate a floating current source

with minimal self heating. This particular configuration can

operate on high supply voltages, determined by the breakdown

voltage of the N-channel JFET.

ADR440/

ADR441/

ADR443/

ADR444/

ADR445

VIN

VOUT

GND

OP90

+VS

SST111

VISHAY

2N3904

–VS

Figure 39. Floating Current Source

PRECISION OUTPUT REGULATOR

(BOOSTED REFERENCE)

ADR440/

ADR441/

ADR443/

ADR444/

ADR445

VIN

VOUT

200

Ω

1µF

2N7002

–V

15V

CIN

0.1µF

COUT

0.1µF

VIN

GND

Figure 40. Boosted Output Reference

Higher current drive capability can be obtained without

sacrificing accuracy by using the circuit in Figure 40. The

operational amplifier regulates the MOSFET turn-on, forcing

VO to equal the VREF. Current is then drawn from VIN, allowing

increased current drive capability. The circuit allows a 50 mA

load; if higher current drive is required, use a larger MOSFET.

For fast transient response, add a buffer at VO to aid with

capacitive loading.

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