Microcontrollers major on capacitive sensing for HMI applications

June 27, 2014 // By Graham Prophet
Silicon Labs’ energy-efficient capacitive sensing microcontrollers (MCUs) are aimed at human-machine interfaces (HMI). The C8051F97x MCU family combines Silicon Labs’ ultra-low-power technology with the industry’s fastest, most accurate capacitive sensing to provide touch control solutions for the Internet of Things, home/building automation, consumer and industrial markets.

Silicon Labs' F97x MCUs offer lowest energy consumption in active, sleep and deep-sleep modes, claiming the longest battery life of any 8-bit capacitive sensing MCUs. With 200 µA/MHz active current, the F97x MCUs combine low energy consumption and system performance. The MCUs’ 2 µsec wake time minimises energy consumption while transitioning from sleep to active mode. The F97x MCUs offer the lowest sleep mode energy consumption in their class: 55 nA sleep current with brownout detector enabled and 280 nA sleep current with a 16.4 kHz internal oscillator.

The F97x MCUs target battery-powered and capacitive touch sensing applications for handheld industrial devices, toys, gaming machines and remote controls, as well as touch-panel switch replacements for white goods such as washers, dryers, ovens and dishwashers.

The F97x MCU family offers capacitive sensing technology with sub-micro-amp (<1 µA) wake-on-touch average current, 16-bit resolution and 100:1 dynamic range to support buttons, sliders, wheels, and capacitive proximity sensing with up to 43 channels and multiple scanning modes. They incorporate Silicon Labs’ SAR charge-timing capacitance-to-digital converter (CDC) technology. The high-resolution CDC’s 40 µsec acquisition time enables fast capacitive touch-sense capability with sensitivity.

Silicon Labs’ CDC technology offers noise immunity for reliable performance in challenging conditions and configurations such as thick laminate overlays, electrical noise or variances in printed circuit board (PCB) manufacturing. This advanced CDC hardware implementation is capable of measuring capacitance on a wide range of materials including PCBs, flex circuits, and indium tin oxide (ITO) on glass and film.

The F97x MCU family has up to 43 capacitive sensing inputs, 32 kB flash memory, 8 kB RAM, seven DMA channels and a 16 x 16 multiply-accumulate (MAC) unit in QFN packages as small as 4 x 4 mm. The F97x MCUs integrate a 25 MHz pipelined 8051-compatible core, a precision oscillator, a 10-bit analogue-to-digital converter (ADC), a temperature sensor, a voltage reference and four 16-bit general-purpose timer/counters.

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