SX8661 datasheet(21/88 Pages) SEMTECH

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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

In the Strongest-mode the strongest touched button will be reported on the AOI and the I2C. All touches that

occur afterwards representing a weaker touch will not be reported. Only a touch which is stronger will be reported

by the SX860.

Figure 16 shows the Strongest-mode reporting in case of 2 touches (with bt1 the strongest touch).

Figure 16

Strongest-mode reporting with 2 touches

At time t1 button0 is touched and reported on the AOI. At time t2 button1 is touched as well. As bt1 is the

strongest touch it will be reported on the AOI immediately (or after one scan period at idle level). At time t3 the

button0 is released while the AOI continues to report button1. At time t4 both buttons are released and the AOI

reports the idle level.

In some special cases (when the buzzer is suspected to load heavily the power supply) the user may choose the

AOI to go to 0V, to VDD or to the AOI idle level for the duration the buzzer is active.

Figure 17

AOI behavior with 0V buzzer state

In Figure 17 the AOI will go to 0V each time the buzzer is active. The AOI returns then to either the idle mode for

one scan period or goes immediately to the PWM button level.

In case the SX8661 is set to sleep mode the AOIs will go to 0V.

3.9

Analog Sensing Interface

The Analog Sensing Interface (ASI) converts the charge on the sensors into ticks which will be further digitally

processed. The basic principle of the ASI will be explained in this section.

The ASI consists of a multiplexer selecting the sensor, analog switches, a reference voltage, an ADC sigma delta

converter, an offset compensation DAC and an external integration capacitor (see Figure 18).

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