sx8636 Semtech Corporation, sx8636 Datasheet - Page 14

• Manufacturer Part Number: sx8636
• Description: Low Power, Capacitive Button Touch Controller 8 Sensors With Enhanced Led Drivers And Proximity Sensing
• Manufacturer: Semtech Corporation

SX8636
Low Power, Capacitive Button Touch Controller (8 sensors)
with Enhanced LED Drivers and Proximity Sensing
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
3.5 Sensors on the PCB
The capacitive sensors are relatively simple copper areas on the PCB connected to the eight SX8636 capacitive
sensor input pins (CAP0…CAP7).The sensors are covered by isolating overlay material (typically 1mm...3mm).
The area of a sensor is typically one square centimeter which corresponds about to the area of a finger touching
the overlay material.
The capacitive sensors can be setup as ON/OFF buttons for either touch or proximity sensing (see example
Figure 9).
layer of three touch buttons sensors
Figure 9 PCB top
surrounded by a proximity sensor
Please refer to the layout guidelines application note [1], for more details.
3.6 Button Information
3.6.1
Button Information
The touch buttons have two simple states (see Figure 10): ON (touched by finger) and OFF (released and no
finger press).
Buttons
Figure 10
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.
Buttons can also be used to do proximity sensing. The principle of proximity sensing 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.
Revision 7_5, September 10
© 2010 Semtech Corp.
www.semtech.com
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