2.6 Full-Scale Adjustment

In the case where the matching of R

accuracy in a particular application, the V

adjusted or an external resistor and potentiometer can be

added as shown in

Figure 10 to provide a full-scale adjust-

ment.

The temperature coefficients of the resistors used for this

adjustment are of an important concern. To prevent degra-

dation of the gain error temperature coefficient by the exter-

nal resistors, their temperature coefficients ideally would

have to match that of the internal DAC resistors, which is a

highly impractical constraint. For the values shown in

Figure

10, if the resistor and the potentiometer each had a tempera-

error temperature coefficent would be degraded a maximum

of 0.0025%/˚C for an adjustment pot setting of less than 3%

of R

2.7 Using the DAC0830 in a Voltage Switching

Configuration

The R-2R ladder can also be operated as a voltage switch-

ing network. In this mode the ladder is used in an inverted

manner from the standard current switching configuration.

The reference voltage is connected to one of the current

output terminals (I

for complementary binary) and the output voltage is taken

from the normal V

voltage in the range from 0V to 255/256 V

of the applied digital code as shown in

Figure 11.

00560840

Input Code

IDEAL V

OUT

MSB

LSB

+V

REF

−V

REF

1 1111111

1 1000000

1 0000000

0 1111111

0 0111111

0 0000000

*THESE RESISTORS ARE AVAILABLE FROM BECKMAN INSTRUMENTS, INC. AS THEIR PART NO. 694-3-R10K-D

FIGURE 9.

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