FDC2214: FDC2214 distance problem

Hello,

The detection range of the FDC2214 depends on 3 primary factors:

1. Size of the sensor: Larger sensors have a longer detection range. Refer to the following application note for more info: http://www.ti.com/lit/pdf/SNOA940
2. How capacitive the target is: A larger object can be detected further away than a smaller object because it produces a larger capacitive shift to the device
3. The level of noise in the system: Having a smaller amount of noise in the system allows you to pickup smaller signals which translates to a further detection range. Typically noise is determined by the quality of the sensor components, reference oscillator, and length of measurement.

1. 1. Sensor components: Using high Q sensor components like a PCB spiral inductor, small value C0G capacitor for the sensor provide a very stable oscillator. 
   2. Reference oscillator: Using a high quality external oscillator will reduce the variation in output code especially compared to internal oscillator. The key parameters are the nominal frequency and the frequency stability. The FDC2214EVM uses a 40MHz oscillator with ±50ppm frequency stability from CTS Electrocomponents (625L3C040M00000).
   3. Length of time for measurement: This is controlled by the RCOUNT. Having a higher RCOUNT means sampling for a longer time which gives the device more time to make a stable / accurate measurement. Refer to the following application note for a better understanding of the resolution: http://www.ti.com/lit/pdf/SNOA944 

And always the best way to determine the detection range is to buy an FDC2214EVM and test with larger sensor surface area. Sensors can be constructed out of a wide range of conductors including a copper plane from a PCB layer, aluminum foil, or copper tape for example. 

Hope this helps point you in the right direction!

Regards,

Luke