Table 1. Resistor-Value Selection for the Figure 4 Circuit to Achieve 0.5% Accuracy

Output

(volts)

R1

(kilohms)

R2

(kilohms)

(kilohms)

Accuracy

(percent)

2.048

200

301

50

0.5

2.500

309

301

50

0.5

4.096

732

301

50

0.5

5.000

976

301

50

0.5

Fine Adjustment over a Wide Voltage Range

Figure 5 combines the MAX6160 with the MAX5415 (a dual, 100-kilohm, 256-tap digital pot) to

achieve a fine adjustment over a wide output-voltage range. Due to the symmetry in this circuit,

there is some redundancy, making only 25% of the settings unique. With this interesting

topology, the output can be set to within 0.06% of 2.048V, 0.03% of 2.500V, 0.08% of 4.096V,

and 0.2% of 5.00V. Because of the interaction between the two pots, the transfer function is

nonlinear in two dimensions, resulting in a response that resembles a saddle. A plot of this is

shown in Figure 6, where 32-tap digital pots are used instead of 256-tap digital pots for clarity.

Figure 5. The MAX6160 digitally adjustable voltage reference with the MAX5415, dual, 100-

kilohm, 256-tap digital pot