SX8644I05AWLTRT Semtech, SX8644I05AWLTRT Datasheet - Page 19

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

ADVANCED COMMUNICATIONS & SENSING
3.9 Processing
The first processing step of the raw ticks, coming out of the ASI, is low pass filtering to obtain an estimation of the
average capacitance: tick-ave (see Figure 17).
This slowly varying average is important in the detection of slowly changing environmental changes.
The difference of the tick average and the raw ticks, tick-diff, is a good estimation of rapid changing input
capacitances.
The tick-diff, tick-ave and the configuration parameters in the SPM are then processed and determines the sensor
information, I2C registers status and PWM control.
3.10 Configuration
Figure 18 shows the building blocks used for configuring the SX8644.
The default configuration parameters of the SX8644 are stored in the Quick Start Memory (QSM). This
configuration data is setup to a very common application for the SX8644 with 6 buttons and a slider. Without any
programming or host interaction the SX8644 will startup in the Quick Start Application.
Revision 7_3, January 10
ASI
processing
compensation DCV
ticks (raw)
low pass
Touch Controller (12 sensors) with Enhanced LED Drivers
© 2009 Semtech Corp.
Figure 18
Figure 17
tick-ave
tick-diff
Configuration
19
Processing
Ultra Low Power, Capacitive Button and Slider
processing
SPM
PWM LED
controller
controller
GPIO
I2C
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SX8644