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Positive Voltage Output Circuit

V

OUT

R

FB

C

1

0

V

+2.5V

£

£

OUT

GND

GND

-2.5V

V

OUT

V

IN

V

REF

+2.5VReference

V

DD

V

DD

DAC7811

OPA277

OPA277

I

2

OUT

I

1

OUT

Bipolar Output Section

V

OUT

+

D

0.5

1

V

REF

(2)

I

1

OUT

R

FB

C

1

GND

V

DD

V

DD

+2.5V

(+10V)

V

REF

V

OUT

C

2

U3

OPA277

10kW

10kW

5kW

-

£

£

2.5V

V

OUT

+2.5V

(-

£

10V

V

U2

OPA277

DAC7811

I

2

OUT

DAC7811

SBAS337C – APRIL 2005 – REVISED JULY 2007

As Figure 30 illustrates, in order to generate a positive voltage output, a negative reference is input to the

DAC7811. This design is suggested instead of using an inverting amp to invert the output as a result of resistor

and a –2.5V input to the DAC7811 with an op amp.

Figure 30. Positive Voltage Output Circuit

The DAC7811, 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 31,

external op amp U3 is added as a summing amp and has a gain of 2X that widens the output span to 5V. A

4-quadrant multiplying circuit is implemented by using a 2.5V offset of the reference voltage to bias U3.

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 31.

Figure 31. Bipolar Output Circuit

16

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