Hello,
I am using the FDC2114 for capacitance measurements and face some issues concerning an amplitude warning in the DATA register. As described in the data sheet (p.28), "If the amplitude has not settled prior to the conversion start, an Amplitude warning will be generated if reporting of this type of warning is enabled." Therefore, I tried to adjust the correct value in the SETTLECOUNT register.
My first approach was to calculate the correct value. SETTLECOUNT must be configured as in equation (4), p. 17 in the data sheet.
- IDRIVE is configured as 0,038 mA as I measure 1,61 V on IN1B vs ground and 1,35 V on IN1A vs ground.
- The sensor capacitance is 27 pF, but I am not sure about the parasitic PCB capacitance. Therefore, I used 150 pF for the calculation as the datasheet states that SETTLECOUNT must be programmed to be at least the value calculated from equation (4).
- The reference frequence is 2,4 MHz
The SETTLECOUNT value, I obtain from equation (4), is 5. To give some extra settling time, I programmed the SETTLECOUNT register to 6. With this configuration, I read out an amplitude warning in the DATA register.
My second approach was to vary the SETTLECOUNT register from 0x0000 to 0xFFFF (where all other register values were fixed). I tried out about 20 values in the possible range, but I always read out an amplitude warning in the DATA register.
Can you kindly give support about the amplitude warning?
Related to the above issue, I also checked if I can read back the correct register values. I observed some strange behaviour concerning the reserved area in the DRIVE_CURRENT registers. When I read back the DRIVE_CURRENT register, I do not obtain b000 0000 0000 in the reserved area and I am not sure if this is an issue. I know from the data sheet (p.22) that "fields indicated with Reserved must be written only with indicated values." Can you please give advice if this is an expected behaviour or if this should be investigated further?
I appreciate your support.
Best regards,
Andrea