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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

Hi,

 

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

 

Oliver

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