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APPLICATION INFORMATION

Stability Circuit

GND

I

1

OUT

R

FB

V

REF

V

REF

V

DD

V

DD

V

OUT

I

2

OUT

C

1

U1

U2

Positive Voltage Output Circuit

GND

-2.5V

+2.5 V Reference

OPA277

GND

I

1

OUT

R

FB

0

V

<

OUT

+2.5 V

<

V

OUT

V

REF

V

DD

V

IN

V

DD

V

OUT

I

2

OUT

C

1

OPA277

DAC7821

Bipolar Output Section

)(V

D

0.5

)1

V

REF

(2)

DAC7821

SBAS365A – OCTOBER 2005 – REVISED FEBRUARY 2006

inverting node of the op amp should be as short as possible and according to correct printed circuit board (PCB)

layout design. For each code change, there is a step function. If the gain bandwidth product (GBP) of the op amp

is limited and parasitic capacitance is excessive at the inverting node, then gain peaking is possible. Therefore,

Figure 27.

Figure 27. Gain Peaking Prevention Circuit with Compensation Capacitor

As Figure 28 illustrates, in order to generate a positive voltage output, a negative reference is input to the

DAC7821. This design is suggested instead of using an inverting amp to invert the output as a result of resistor

and a –2.5 V input to the DAC7821 with an op amp.

Figure 28. Positive Voltage Output Circuit

The DAC7821, 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 29,

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

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