Tool/software:
Hi,
This is a repeat of some issues that I've seen on the forum:
FDC1004: Different capacitance value measured when CAPDAC change
I have the same problem and need a solution.
I have a sensor that is used to measure water depth on channel 3. The peak capacitance on the channel will be approx. 70 pF. I'm working in the Arduino framework with custom hardware and sensor PCB. The driver can be seen github.com/.../FDC1004 As the water depth increases, the driver increases the CAPDAC value, and the resulting capacitance increases linearly until the CAPDAC changes from 16 to 17. At that point, the channel capacitance decreases by more than one CAPDAC stop, causing a discontinuity in the capacitance reading. It looks to decrease by an additional 3.88 pF above the CAPDAC extra 3.125 pF expected from the CAPDAC increase. I think there is also a similar effect when changing from 8 to 9 but to a lesser extent.
From what I can see it's something in the chip that's causing it. Looking a the forums, similar issues have been reported but no conclusions have been reached.
Can you please help resolve the issue and define a clean workaround. I've added an image to show the glitch as I see it from the sensor we have. I've check all connections and power rail as well as parasitics etc. The sensor is an FR4 PCB layout with the FDC1004 surface mounted so I'm confident it not the sensor it's the FDC1004 or how we are driving it. The issue appears across all channels and always CADPAC 8 to 9 or 16 to 17
Many thanks
Neale.
