SX8663 datasheet(10/64 Pages) SEMTECH

10 / 64 page

ADVANCED COMMUNICATIONS & SENSING

Rev5 4

th August 2011

www.semtech.com

SX8663

Capacitive Button Matrix (up to 36) and Proximity Controller

with Individual LED Drivers and Buzzer Output

FUNCTIONAL DESCRIPTION

3.1

Introduction

3.1.1

General

The SX8663 is intended to be used in applications which require capacitive sensors covered by isolating overlay

material. A finger approaching the capacitive sensors will change the charge that can be loaded on the sensors.

The SX8663 measures the change of charge and converts that into digital values (ticks). The larger the charge on

the sensors, the larger the number of ticks will be. The charge to ticks conversion is done by the SX8663 Analog

Sensor Interface (ASI).

The ticks are further processed by the SX8663 and converted in a high level, easy to use information for the

user’s host.

The information between SX8663 and the host is passed through the I2C interface with an additional interrupt

signal indicating that the SX8663 has new information. For buttons this information is simply touched or released.

User feedback, done through the SX8663’s GPIOs, can be visual via LEDs and/or audio via a buzzer.

3.1.2

Parameters

The SX8663 has many low level built-in, fixed algorithms and procedures. To allow a lot of freedom for the user

and adapt the SX8663 for different applications these algorithms and procedures can be configured with a large

set of parameters which will be described in the following sections.

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.

3.1.3

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

SX8663 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 SX8663. The programming needs to be done once (over the I2C). The SX8663 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.

3.2

Scan Period

The basic operation Scan period of the SX8663 sensing interface can be split into three periods over time.

In the first period (Sensing) the SX8663 is sensing all enabled CAP inputs, from CAP0 towards CAP11.

In the second period (Processing) the SX8663 processes the sensor data, verifies and updates the GPIO and the

I2C.

In the third period (Timer) the SX8663 is set in a low power mode and waits until a new cycle starts.

Figure 6 shows the different SX8663 periods over time.

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