This document describes design aspects which should be considered for application circuits using NXP capacitive sensors.
This document describes design aspects that should be considered for application circuits using NXP capacitive sensors. It covers typical application circuits for the PCF8885 and PCA8885 chips, providing a pin-by-pin analysis with recommended component values and additional remarks not found in the standard data sheets.
The note further details design considerations for sensor plates, explaining how to maximize sensitivity by maximizing capacitance between the finger and the plate while minimizing stray capacitance to ground. It includes theoretical background, simulation results regarding stray capacitance, and specific guidelines for handling unused sensor channels to manage current consumption.
The input capacitance range of the PCx8885 is 10 pF to 40 pF.
In the default settings, the oscillator frequency is 70 kHz.
It will take 117 ms to define a capacitive event with a sampling frequency of 0.55 kHz.