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AD7568: Input impedance

AD7568 uses R-2R ladder, my customer wants to know what is the value of the R
used in the ladder.


The input impedance of the R-2R DAC is R, that's inherent in the design. See
figure 13 in datasheet working from right to left.

2R || 2R = R
R+R|| 2R = R etc etc.

So R of ladder is equal to input resistance which varies from a min of 5K to a
max of 9K with a typical of 7K.

Please note your simulation may need to do a Monte Carlo analysis/simulation
with R_tolerance/temperature in mind.