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Bipolar Output Circuit

V

OUT

+

D

16, 384 *

1

V

REF

(2)

R

FB

OPA277

U4

10 kW

10 kW

+2.5 V

GND

DAC8801

OPA277

U2

C1

C2

5 kW

−

+

−

+

(+10 V)

Programmable Current Source Circuit

I

(R2

) R3)

R1

R3

V

REF

D

(3)

DAC8801

U1

OPA277

U2

GND

150 kW

R14

15 kW

R24

C1

10 pF

OPA277

U2

15 kW

R2

50 W

R34

50 W

R3

150 kW

R1

LOAD

−

+

+

−

DAC8801

SLAS403B – NOVEMBER 2004 – REVISED FEBRUARY 2007

APPLICATION INFORMATION (continued)

The DAC8801, as a 2-quadrant multiplying DAC, can be used to generate a unipolar output. The polarity of the

Some applications require full 4-quadrant multiplying capabilities or bipolar output swing. As shown in Figure 22,

external op amp U4 is added as a summing amp and has a gain of 2X that widens the output span to 5 V. A

4-quadrant multiplying circuit is implemented by using a 2.5-V offset of the reference voltage to bias U4.

According to the circuit transfer equation given in Equation 2, input data (D) from code 0 to full scale produces

Figure 22. Bipolar Output Circuit

A DAC8801 can be integrated into the circuit in Figure 23 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. A application of this circuit includes a 4-mA to 20-mA current transmitter with up to a 500-

Ω load.

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

Figure 23. Programmable Bidirectional Current Source Circuit

11

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