Table 1. Resistor-Value Selection for the Figure 4 Circuit to Achieve 0.5% Accuracy
R
P
Output
R1
R2
Accuracy
(volts) (kilohms) (kilohms) (kilohms) (percent)
2.048
2.500
4.096
5.000
200
309
732
976
301
301
301
301
50
50
50
50
0.5
0.5
0.5
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