Hi Li min,
The raw counts majorly depends on the capacitance of the sensor and minorly depends on internal parameters like clock accuracy, IDAC current, voltage changes etc.
Please refer page number 35 of the following application note which tells you about the formula for calculating the raw counts.
In case you want to compensate the effects of drift in raw counts due to temperature variation, please refer the following KBA
Hope this helps !
In addition to that, you can increase the baseline coefficient value so that baseline quickly tracks any temperature change and will detect the finger touch events reliably. But please note that, if you increase the baseline coefficient, then it might be difficult to detect slowly approaching fingers on the buttons.
Dear Ganesh & Bragadeesh:
HW is confirmed by customer, can't add reference sensor now.
Modified baseline coefficient value might cause detect error for slowly approaching fingers on the buttons.
We now decide to sample the raw count & base line in room temperture(25 deg) to check if FT & HY is good. For equipment limit and operator healthy, we can't do same job in Low & High temp(-20 & 80 deg. Can we use same FT & HY (Checked in room temp) for all temperture range?
Sure, we will check in all temperture rang.