sx8638 Semtech Corporation, sx8638 Datasheet - Page 19

• Manufacturer Part Number: sx8638
• Description: Low Power, Capacitive Button And Slider Touch Controller 8 Sensors With Enhanced Led Drivers And Proximity
• Manufacturer: Semtech Corporation

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 SX8638.
The default configuration parameters of the SX8638 are stored in the Quick Start Memory (QSM). This
configuration data is setup to a very common application for the SX8638 with buttons and a slider. Without any
programming or host interaction the SX8638 will startup in the Quick Start Application.
Revision 7_6, September 10
ASI
processing
compensation DCV
ticks (raw)
low pass
© 2010 Semtech Corp.
Low Power, Capacitive Button and Slider Touch Controller
Figure 18
Figure 17
(8 sensors) with Enhanced LED Drivers and Proximity
tick-ave
tick-diff
Configuration
19
Processing
processing
SPM
PWM LED
controller
controller
GPIO
I2C
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SX8638