32.2 Overview

The Peripheral Touch Controller (PTC) detects touch inputs on capacitive sensors. The external capacitive touch sensor is typically formed on a printed circuit board (PCB) or a transparent conductive substrate made of a transparent or translucent material, such as indium tin oxide (ITO) or poly (3,4-ethylenedioxythiophene) (PEDOT). An increasingly popular implementation is printing the sensor electrodes directly on the backside of the touch surface using conductive inks. The sensor electrodes are connected to the PTC through the I/O pins in the device. The PTC supports both mutual and self-capacitance sensors. Figure 32-1 shows some examples of the supported touch sensors .

A self-capacitance sensor consists of a conductor plate with one wire connected directly to an I/O pad. In Self-Capacitance mode, the PTC requires one pin (Y-line) for each touch sensor. See the Figure 32-2.

A mutual capacitance sensor consists of two conductor plates, each connected to an I/O pad. Driving one plate, and sensing the other one measures the mutual capacitance between the two plates. In Mutual Capacitance mode, sensing is performed using capacitive touch matrices supporting various X-Y configurations. The PTC requires one pin per X-line and one pin per Y-line. See the Figure 32-3.

For a capacitive matrix array where only a single touch point is needed, self-capacitance sensing on both vertical and horizontal lines can effectively identify the touch point by locating the intersection of the touched lines. However, for multiple touch points, self-capacitance scanning alone is insufficient for accurately determining their exact positions. To precisely detect multiple touch points, mutual-capacitance sensing is required.

The number of available pins and the assignment of X- and Y-lines depend on both package type and device configuration.

For more information about designing the touch sensor, refer to the AN2934, “Capacitive Touch Sensor Design Guide (DS00002934)”.