SX8645I05AWLTRT Semtech, SX8645I05AWLTRT Datasheet - Page 11

• Manufacturer Part Number: SX8645I05AWLTRT
• Description: 12-ch Capacitive Touch Solution (Button & Wheel)
• Manufacturer: Semtech

ADVANCED COMMUNICATIONS & SENSING
The information between SX8645 and the user’s host is passed through the I2C interface with an additional
interrupt signal indicating that the SX8645 has new information. For buttons this information is simply touched or
released.
3.2.2
A second path of feedback to the user is using General Purpose Input Output (GPIO) pins. The SX8645 offers
eight individual configurable GPIO pins. The GPIO can e.g. be set as a LED driver which slowly fade-in when a
finger touches a button and slowly fade-out when the button is released. Fading intensity variations can be
logarithmic or linear. Interval speed and initial and final light intensity can be selected by the user. The fading is
done using a 256 steps PWM. The SX8645 has eight individual PWM generators, one for each GPIO pin.
The LED fading can be initiated automatically by the SX8645 by setting the SX8645 Autolight feature. A simple
touch on a sensor and the corresponding LED will fade-in without any host interaction over the I2C.
In case the Autolight feature is disabled then the host will decide to start a LED fading-in period, simply by setting
the GP0 pin to ‘high’ using one I2C command. The SX8645 will then slowly fade-in the LED using the PWM
autonomously.
In case the host needs to have full control of the LED intensity then the host can set the GPIO in GPP mode. The
host is then able to set the PWM pulse width freely at the expense of an increased I2C occupation.
The GPIOs can be set further in the digital standard Input mode (GPI).
3.2.3
The SX8645 has many low level built-in, fixed algorithms and procedures. To allow a lot of freedom for the user
and adapt the SX8645 for different applications these algorithms and procedures can be configured with a large
set of parameters which will be described in the following sections. Examples of parameters are which sensors
are buttons or which sensors are parts of a wheel, which GPIO is used for outputs or LEDs and which GPIO is
mapped to which button.
Sensitivity and detection thresholds of the sensors are part of these parameters. Assuming that overlay material
and sensors areas are identical then the sensitivities and thresholds will be the same for each sensor. In case
sensors are not of the same size then sensitivities or thresholds might be chosen individually per sensor.
So a smaller size sensor can have a larger sensitivity while a big size sensor may have the lower sensitivity.
3.2.4
During a development phase the parameters can be determined and fine tuned by the users and downloaded
over the I2C in a dynamic way. The parameter set can be downloaded over the I2C by the host each time the
SX8645 boots up. This allows a flexible way of setting the parameters at the expense of I2C occupation.
In case the parameters are frozen they can be programmed in Multiple Time Programmable (MTP) Non Volatile
Memory (NVM) on the SX8645. The programming needs to be done once (over the I2C). The SX8645 will then
boot up from the NVM and additional parameters from the host are not required anymore.
In case the host desires to overwrite the boot-up NVM parameters (partly or even complete) this can be done by
additional I2C communications.
Revision 7_5, February 10
GPIOs
Parameters
Configuration
Touch Controller (12 sensors) with Enhanced LED Drivers
© 2010 Semtech Corp.
11
Ultra Low Power, Capacitive Button and Wheel
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SX8645