SX8644I05AWLTRT Semtech, SX8644I05AWLTRT Datasheet - Page 15

• Manufacturer Part Number: SX8644I05AWLTRT
• Description: 12-ch Capacitive Touch Solution (Button & Slider)
• Manufacturer: Semtech

ADVANCED COMMUNICATIONS & SENSING
3.6 Button and Slider Information
3.6.1
The buttons have two simple states (see Figure 11): ON (touched by finger) and OFF (released and no finger
press).
A finger is detected as soon as the number of ticks from the ASI reaches a user-defined threshold plus a
hysteresis.
A release is detected if the ticks from the ASI go below the threshold minus a hysteresis. The hysteresis around
the threshold avoids rapid touch and release signaling during transients.
3.6.2
In case sensors are arranged in a slider configuration the ON, OFF information remains available as if it would be
a single sensor button.
Wherever the slider is touched the information will be set to ON. If no finger is present the slider information will be
OFF.
Due to the 2 dimensional character of the slider more information can be derived by processing the ticks.
During a touch a finger will influence most of the time the charge on one or two sensors but never all of the
sensors at the same time. Some sensor ticks will be larger than others based on the finger position.
The processing algorithms can therefore determine where the finger is positioned on the slider.
Interpolation between sensors increases the resolution beyond the number of sensors in the slider.
The interpolation can be done already on the PCB sensor structures (analog, like the chevron slider in Figure 10)
and as well by SX8644 digital processing of the ticks using center of gravity calculations.
The position of the finger on the PCB structures varies between the minimum zero and a user defined maximum
(Figure 13).
Revision 7_3, January 10
Button Information
Slider Information
Touch Controller (12 sensors) with Enhanced LED Drivers
Figure 12
© 2009 Semtech Corp.
Figure 13
min
Figure 11
position
Slider ON, OFF
....x...
Slider Position
15
Ultra Low Power, Capacitive Button and Slider
Buttons
max
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SX8644