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Programmable Current Source Circuit

I

(R2

)R3)

R1

R3

V

REF

D

4096

(3)

Z

O

+

R1 R3

(R1)R2)

R1

(R2 )R3 ) * R1 (R2)R3)

(4)

R2¢

15kW

I

1

OUT

R

FB

GND

V

DD

V

DD

V

REF

I

L

LOAD

C

1

10pF

U3

OPA277

R1¢

150kW

R3¢

50W

R3

50W

R1

150kW

R2

15kW

U2

OPA277

U1

DAC7811

I

2

OUT

Cross-Reference

DAC7811

SBAS337C – APRIL 2005 – REVISED JULY 2007

A DAC7811 can be integrated into the circuit in Figure 32 to implement an improved Howland current pump for

precise voltage to current conversions. Bidirectional current flow and high voltage compliance are two features of

the circuit. With a matched resistor network, the load current of the circuit is shown by Equation 3:

The value of R3 in Equation 3 can be reduced to increase the output current drive of U3. U3 can drive

±20mA in

both directions with voltage compliance limited up to 15V by the U3 voltage supply. Elimination of the circuit

according to Equation 4:

value of several pF is suggested.

Figure 32. Programmable Bidirectional Current Source Circuit

The DAC7811 has an industry-standard pinout. Table 5 provides the cross-reference information.

Table 5. Cross-Reference

SPECIFIED

TEMPERATURE

PACKAGE

PACKAGE

CROSS-

PRODUCT

INL (LSB)

DNL (LSB)

RANGE

DESCRIPTION

OPTION

REFERENCE PART

DAC7811

±1

±1

–40

°C to +125°C

10-Lead MicroSOIC

MSOP-10

AD5443YRM

17

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