AnsweredAssumed Answered

AD7746 measurement problem

Question asked by Sandman on Dec 15, 2015
Latest reply on Dec 17, 2015 by EricC

Hi , I'm trying to use the AD7746 to measure a capacitance about 30pF, I used the extension circuit, F is about  7.6

 

but the AD7746 is feeding me with [00 00 00] (0x01, 0x02, 0x03) when the CAPDAC+ is enabled, and I tried different numbers, same issue. when I get the CAPDAC down to about 0, the CAP DATA REGISTER start providing numbers less than [80 00 00], which leads to negative capacitance reading.

 

and I also tried to use the single-ended circuit in Figure 30 on AD7746 spec, still I got numbers less than [80 00 00].

I'm wondering if it's possible my chip is damaged? Can anybody help me with this? Thanks.

I got some pictures attached

222.jpg

Outcomes