This application note explains the unique auto-calibration feature of the touch sensor family from NXP and provides guidelines for enhanced water and condensation safe operation, focusing on applications with capacitive touch buttons
This document details the unique auto-calibration technology used by NXP's PCF8883, PCA8885, PCF8885, and PCA8886 capacitive touch sensors. This patented feature digitally filters out slow changes in capacitance caused by dirt, humidity, or temperature variations, preventing false switches that affect other sensor types.
The guide provides specific guidelines for enhancing water and condensation safety in applications with capacitive touch buttons. It covers strategies to handle static water droplets and sudden water flashes (overflows), recommending design practices such as increasing the gap between sensor plates and ground rings, using conductive extensions, and monitoring reservoir capacitor voltage.
The devices digitally filter out very slow and very quick changes in capacitance at the input, making performance less affected by dirt, humidity, or freezing temperatures.
It is recommended that the gap be kept larger than the overlay thickness, though a 2.2 mm gap is sufficient even if the overlay is thicker than 2 mm.
The system should monitor the reservoir capacitor voltage to inform management of an overflow, utilizing a trade-off between safety and touch sensitivity.