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AD7190 unbuffered RC data sheet values background?

Question asked by obetz on Aug 6, 2015
Latest reply on Aug 28, 2015 by obetz



the AD7190 data sheet Table 22 states 5 R-C-combinations for unbuffered operation.


I tried to understand the background of the values but they look non-monotonic: The second last entry (1000pF 230Ohms) has a longer time constant than the last entry.


The total attenuation should be the something like


(Cext / Cint) * exp(tmod / RC)


where tmod is a fraction of the modulator cycle (3,2us), isn't it?


It would be helpful to get some information on the reason behind table 22. And information about the behaviour in unbuffered PGA>1 configurations.


What will be the common mode and differential impedance if I use a huge filter capacitor, i.e. 10uF?


Thanks in advance