29.6.4 PTC Analog Front End (AFE)

The analog front end consists of X-line drivers, a sensor capacitance compensation circuit and a parasitic capacitance insensitive analog Switched Capacitor Charge Integrator (SCCI). The integrator is connected to sensor Y-lines via an analog multiplexer. When the PTC digital controller is enabled, the SCCI output is automatically connected to the ADC input.

The external capacitive touch sensor is typically formed on a PCB and the sensor electrodes are connected to the Analog Charge Integrator of the PTC AFE via MCU I/O port pins. The PTC AFE supports mutual capacitance sensors organized as capacitive touch matrices in different X-Y configurations (QTouch Surface). The PTC AFE requires one pin per X-line and one pin per Y-line. No external components are needed.

The PTC AFE also supports “self-capacitance touch sensors” (QTouch). In Self-capacitance mode, the PTC AFE requires just one Y-line pin per self-capacitance sensor.