SX8661Z datasheet(13/87 Pages) SEMTECH

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ADVANCED COMMUNICATIONS & SENSING

DATASHEET

Revision v4.0, February 2016

www.semtech.com

SX8661Z

Low Power, Capacitive Button Touch and Proximity Controller

(8 sensors) with LED Drivers and Analog Output

3.1.5

Parameters

The SX8661Z has many low level built-in, fixed algorithms and procedures. To allow a lot of freedom for the user

and adapt the SX8661Z 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, which GPIO is used for outputs, for the Analog Output Interfaces, the Buzzer 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.

3.1.6

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

SX8661Z 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 SX8661Z. The programming needs to be done once (over the I2C). The SX8661Z 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 SX8661Z sensing interface can be split into three periods over time.

In the first period (Sensing) the SX8661Z is sensing all enabled CAP inputs, from CAP0 towards CAP7.

In the second period (Processing) the SX8661Z processes the sensor data, verifies and updates the GPIO and

the I2C.

In the third period (Timer) the SX8661Z is set in a low power mode and waits until a new cycle starts.

Figure 6 shows the different SX8661Z periods over time.

sensing

data

processing

timer

scan period

time

timer

Figure 6

Scan Period

The scan period determines the minimum reaction time of the SX8661Z. The scan period can be configured by

the host from 15ms to values larger than a second.

The reaction time is defined as the interval between a touch on the sensor and the moment that the SX8661Z

generates the interrupt on the INTB pin. The shorter the scan period the faster the reaction time will be.

Very low power consumptions can be obtained by setting very long scan periods with the expense of having

longer reaction times.

All external events like GPIO, I2C and the interrupt are updated in the processing period, so once every scan

period.

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