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Capacitive to digital converter delivers superior gesture sensing

A touch/proximity sensing solution from ON Semiconductor – the LC717A30UJ high dynamic range capacitance-to-digital converter – uses mutual capacitance to detect changes in capacitance down to femtofarad levels.

Parasitic capacitance cancellation raises the detector sensitivity, while its built-in noise rejection mechanism combats the effects of electromagnetic interference. The eight capacitance-sensing input channels is said to make the LC717A30UJ highly optimised for use in systems where an array of switches is required.

The device includes an integrated multiplexer for input channel selection, analogue-to-digital converter, dual-stage amplifier that determines capacitance changes plus outputs analogue amplitude values, system clock, power-on reset circuit, and all the necessary control logic to create a total solution. Both I2C and SPI interfaces are selectable.

The device’s sensitivity has a range of 150mm, which enables gesture motions as well as offering conventional touch functionality. In addition, it can operate with an airgap between the sensor/PCB and the protective cover so engineers can eliminate the inclusion of a light guide.

This device also includes an integrated automatic calibration function which optimises and self-calibrates total capacitance according to electrode, line capacitance, and surrounding environment.

The LC717A30UJ delivers a measurement time of 16ms for its eight sensing channels and runs off a 2.6V to 5.5V supply with a low power standby mode of 1µA. It is AEC-Q100 compliant.

The device can be employed in a range of touch or gesture human interfaces in industrial and consumer end products such as induction cookers, refrigerators, home entertainment systems, building automation equipment, industrial equipment, and lighting controls.

Peggy Lee

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