www.ti.com

GND

OPA277

−2.5V

GND

OPA277

C1

DAC8811

+2.5V Reference

−

+

−

+

Bipolar Output Circuit

V

OUT

+

D

32, 768 *

1

V

REF

(2)

R

FB

OPA277

U4

10 kW

10 kW

+2.5V

(+10V)

GND

DAC8811

OPA277

U2

C1

C2

5 kW

−

+

−

+

Programmable Current Source Circuit

I

(R2

)R3)

R1

R3

V

REF

D

(3)

DAC8811

SLAS411A – NOVEMBER 2004 – REVISED DECEMBER 2004

APPLICATION INFORMATION (continued)

Figure 21. Positive Voltage Output Circuit

The DAC8811, 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

External resistance mismatching is the significant error in Figure 22.

Figure 22. Bipolar Output Circuit

A DAC8811 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. With a matched resistor network, the load current of the circuit is shown by Equation 3:

10