Capacitive-to-digital converter senses gestures up to 150 mm away

January 17, 2017 // By Christoph Hammerschmidt
With a new capacitance-to-digital converter, ON Semiconductor facilitates designing gesture sensing and touch interfaces for automotive and industrial systems. The LC717A30UJ features a high degree of integration, a high dynamic range and very low standby current.

The LC717A30UJ uses mutual capacitance to detect changes in capacitance down to femtofarad (fF) levels. Parasitic capacitance cancellation raises the detector sensitivity, while its built-in noise rejection mechanism combats the effects of electromagnetic interference (EMI). Eight capacitance-sensing input channels make the LC717A30UJ highly optimized for use in systems where an array of switches is required. The device includes an integrated multiplexer for input channel selection, A/D converter, a dual-stage amplifier that determines capacitance changes plus outputs analogue amplitude values, system clock, power-on reset circuit, and related control logic. Both I2C and SPI interfaces are selectable based on the application needs.

As the device’s sensitivity has a range of 150 millimeters (mm) - beyond the scope of any competing device on the market – its higher sensitivity enables gesture motions as well as offering conventional touch functionality, thereby enhancing users’ control options to address a wide range of application scenarios. 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 from the assembly and reduce overall complexity. This device also includes an integrated automatic calibration function which optimizes and self-calibrates total capacitance according to electrode, line capacitance, and surrounding environment, thus significantly accelerating system development cycle time as well as robustness.