SX8661 datasheet(14/88 Pages) SEMTECH

14 / 88 page

ADVANCED COMMUNICATIONS & SENSING

DATASHEET

Revision v3.2, January 2011

www.semtech.com

SX8661

Low Power, Capacitive Button Touch and Proximity Controller

(8 sensors) with LED Drivers and Analog Output

3.2

Introduction

3.2.1

General

The SX8661 is intended to be used in applications which require capacitive sensors covered by isolating overlay

material and which need to detect the proximity of a finger/hand though the air. A finger approaching the

capacitive sensors will change the charge that can be loaded on the sensors. The SX8661 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 SX8661 Analog Sensor Interface (ASI).

The ticks are further processed by the SX8661 and converted in a high level, easy to use information for the

user’s host.

The information between SX8661 and the user’s host is passed through the I2C interface with an additional

interrupt signal indicating that the SX8661 has new information. For buttons this information is simply touched or

released. The SX8661 can operate without the I2C and interrupt by using the analog output interface (GPIO7

and/or GPIO6) which voltage level indicates the button touched or GPO with the autolight function.

3.2.2

GPIOs

Feedback to the user is using General Purpose Input Output (GPIO) pins. The SX8661 offers up to 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 or proximity is detected and slowly fade-out when the button is released or finger goes out of

proximity. 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 step PWM. The SX8661 has eight individual PWM

generators, one for each GPIO pin.

The LED fading-in and fading-out mode is called the GPO (fading) mode.

The LED fading can be initiated automatically by the SX8661 by setting the SX8661 autolightening feature. A

simple touch on a sensor and the corresponding LED will fade-in without any host interaction over the I2C.

In case the autolightening feature is disabled then the host will decide to start a LED fading-in period, simply by

setting the GPO pin to ‘high’ using one I2C command. The SX8661 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 the PWM mode

(GPP). 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 special purpose output (SPO) for the buzzer or analog output interface.

3.2.3

Analog Output Interface A and B (SPO mode)

The Analog Output Interface (AOI) is a PWM output signal between ground and VDD. The duty cycle of the AOI

output will change depending on which button is touched. A host controller can then measure the mean voltage

delivered on the AOI output and determine which button is touched at any given time.

The AOI feature allows the SX8661 device to replace directly legacy mechanical button controllers in a quick and

effortless manner. The SX8661 supports up to two Analog Output Interfaces, AOI-A and AOI-B (on GPIO7 and

GPIO6 respectively). The SX8661 allows buttons to be mapped on either AOI-A or AOI-B. The button mapping as

well as the mean voltage level that each button produces on a AOI output can be configured by the user through a

set of parameters described in later chapters (see 5.6).

3.2.4

Buzzer (SPO mode)

The SX8661 can drive a buzzer (on GPIO5) to provide audible feedback on button touches. The buzzer duration

is set to approximately 30ms per default (see 5.7).

3.2.5

Parameters

The SX8661 has many low level built-in, fixed algorithms and procedures. To allow a lot of freedom for the user

and adapt the SX8661 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

SX8661 Datasheet(PDF) 14 Page - Semtech Corporation

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