SX8644 datasheet(11/76 Pages) SEMTECH

Part #	SX8644

Description	Ultra Low Power, Capacitive Button and Slider Touch Controller (12 sensors) with Enhanced LED Drivers

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Manufacturer	SEMTECH [Semtech Corporation]

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ADVANCED COMMUNICATIONS & SENSING

DATASHEET

Revision 7_3, January 10

www.semtech.com

11

SX8644

Ultra Low Power, Capacitive Button and Slider

Touch Controller (12 sensors) with Enhanced LED Drivers

The information between SX8644 and the user’s host is passed through the I2C interface with an additional

interrupt signal indicating that the SX8644 has new information. For buttons this information is simply touched or

released.

3.2.2

GPIOs

A second path of feedback to the user is using General Purpose Input Output (GPIO) pins. The SX8644 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 SX8644 has eight individual PWM generators, one for each GPIO pin.

The LED fading can be initiated automatically by the SX8644 by setting the SX8644 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 SX8644 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

Parameters

The SX8644 has many low level built-in, fixed algorithms and procedures. To allow a lot of freedom for the user

and adapt the SX8644 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 slider, 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

Configuration

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

SX8644 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 SX8644. The programming needs to be done once (over the I2C). The SX8644 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.

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