Sample Capacitor Discharge

The sample capacitor discharge parameter controls whether the sample capacitor is discharged to 0V (empty) or 0.5V (half full). A measurement, or "conversion," is achieved by charging the external capacitor being measured and transferring that charge into an internal sample capacitor multiple times until the internal sample capacitor is full. Having the sample capacitor on-chip reduces the overall system cost. However, on-chip capacitors are not linear when close to empty. By filling the sample capacitor from half full to full, rather than empty to full, a more stable measurement is achievable. The trade-off is that the effective size of the sample capacitor is divided in half. In the case of a very large electrode with a large amount of parasitic capacitance, it is possible to configure the sample capacitor to discharge to 0V rather than 0.5V to increase the sensing range of the system.

Implementation Notes
Sample capacitor discharge should be set to 0.5V (half full) for the majority of applications. Only when the extra range is needed for handling large external capacitors should the sample capacitor be discharged fully to 0V.

Affected Software Parameters
The Sample_Capacitor_Discharge parameter corresponds to the bCsDischarge member of the tSensor type in the CapTIvate Touch Library.