SX8663 datasheet(15/64 Pages) SEMTECH

15 / 64 page

ADVANCED COMMUNICATIONS & SENSING

Rev5 4

th August 2011

www.semtech.com

SX8663

Capacitive Button Matrix (up to 36) and Proximity Controller

with Individual LED Drivers and Buzzer Output

3.5

Button Information (MK and PK)

The touch buttons have two simple states (see Figure 11): ON (touched by finger) and OFF (released and no

finger press).

Figure 11

Buttons

A finger touch is reported as soon as the ASI ticks of both sensors forming the button exceed their user-defined

threshold plus a hysteresis.

A finger release is reported as soon as the ASI ticks of at least one of the sensors forming the button goes below

its user-defined threshold minus a hysteresis.

The hysteresis around the threshold avoids rapid touch and release signalling during transients.

IMPORTANT: Please note that while the matrix structure allows increasing dramatically the potential maximum

number of buttons (up to 36 with only 12 sensors) it also limits the operation to max one matrix button reported at

a time (ie single button touch operation). When two matrix buttons are touched only the first one is reported.

Note that the principle of proximity sensing (PS) operation is exactly the same as for touch buttons except that

proximity sensing is done several centimeters above the overlay through the air. ON state means that finger/hand

is detected by the sensor and OFF state means the finger/hand is far from the sensor and not detected.

3.6

Analog Sensing Interface

The Analog Sensing Interface (ASI) converts the charge on the sensors into ticks which will be further digitally

processed. The basic principle of the ASI will be explained in this section.

The ASI consists of a multiplexer selecting the sensor, analog switches, a reference voltage, an ADC sigma delta

converter, an offset compensation DAC and an external integration capacitor (see Figure 12).

Figure 12

Analog Sensor Interface

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