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THEORY OF OPERATION

R

R

R

R

2R

2R

2R

2R

2R

DB0

(LSB)

DB9

DB10

DB11

(MSB)

I

1

OUT

R

FB

V

REF

I

2

OUT

)(V

OUT

CODE

4096

(1)

OPA277

DAC7821

15V

V+

V-

-15V

GND

I

1

OUT

R

FB

V

REF

V

DD

V

DD

V

OUT

I

2

OUT

DAC7821

SBAS365A – OCTOBER 2005 – REVISED FEBRUARY 2006

The DAC7821 is a single channel current output, 12-bit digital-to-analog converter (DAC). The architecture,

illustrated in Figure 25, is an R-2R ladder configuration with the three MSBs segmented. Each 2R leg of the

potential by the use of an external I/V converter op amp. The R-2R ladder is connected to an external reference

impedance to the external reference of 10 k

Ω ±20%. The external reference voltage can vary over a range of

Figure 25. Equivalent R-2R DAC Circuit

Equation 1:

will also change. Because of this, the external I/V converter op amp must have a sufficiently low offset voltage

with large offset voltages can produce INL errors in the transfer function of the DAC7821 as a result of offset

modulation versus DAC code.

For best linearity performance of the DAC7821, an op amp with a low input offset voltage (OPA277) is

Figure 26. Voltage Output Configuration

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