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AD8226 - ADC Driving for 1kHz Signal

Question asked by henrique on Apr 18, 2017
Latest reply on Jul 10, 2017 by JinoL

Hello, I'm trying to design a circuit as in the bellow figure using the InAmp AD8226, a RC filter and SAR ADC. The signal is a sine wave with a frequency of 1kHz and 3Vp. Reading the page 24 of AD8226 datasheet's , it has a few options for ADC driving and i have two or three questions regarding this subject.
First it says : 

Option 1 shows the minimum configuration required to drive a charge-sampling ADC. The capacitor provides charge to the ADC sampling capacitor while the resistor shields the AD8226 from the capacitance. To keep the AD8226 stable, the RC time constant of the resistor and capacitor needs to stay above 5 µs.

Can you explain me how the designer reached the 5uS  value ? 


The other question is regarding the RC Filter of option 1. Is 1kHz considered an low frequency signal and how did the designer reached the RC network of 100 ohms and 100nF. 


Thank you.