AnsweredAssumed Answered

AD7746 Read value changing

Question asked by jarro on Mar 14, 2014
Latest reply on Mar 19, 2014 by seanbrown

Hello all,

 

I am using the AD7746 to read a small capacitance value. I use both channels but both present an oscillation that will be critical for my application. When I try to read a 4pF capacitor I get a signal that starts around 0.5pF, linearly increases up to 0.7pF and then drops back to 0.5pF almost periodically with a period of around 3 minutes. First, the read capacitance value is way off the real value, it is supposed to be calibrated from factory and my application is very simple so I don't think I should calibrate it but that could be fixed with the DAC and offset. On the other hand, the oscillation is always present. Is there a known issue with this CDC? Attached is a figure showing my problem.Problem.jpg

 

Thank you

Outcomes