Robust capacitive touch switches survive harsh environments
NXP Semiconductors N.V. today announced a complete family of self-calibrating capacitive touch and proximity switches designed for harsh environments. The PCF8883 and PCF8885, along with the automotive-grade PCA8885 and PCA8886, enable robust sensing despite dust, moisture, grease and other types of contamination building up on the touch area, and offer high immunity to sudden temperature changes and to electromagnetic interference. Using digital signal processing to detect changes in capacitance on a remote sensing plate, NXP's capacitive touch switches eliminate the need for a microcontroller and firmware for post-processing. With very low power consumption – typically 3 μA per channel – NXP's capacitive touch and proximity switches can also run continuously, with no complicated power-down and wake-up schemes required.
The sampling frequency and response times are easily adjustable, allowing designers to configure the PCF8883, PCF8885, PCA8885 and PCA8886 for a wide range of industrial and automotive applications. The single-channel PCF8883 and dual-channel PCA8886 can be used as touch switches, or as proximity sensors which wake up and reactivate the system from power-down mode. The multi-channel PCF8885 can be used as a slider, as a rotary wheel and for dedicated touch keys.
NXP's highly robust capacitive touch and proximity switches are ideal for applications using touch screen control panels, including:
- Home appliances such as washing machines, ovens and vacuum cleaners
- Building control systems for heating, ventilation and air conditioning (HVAC) and lighting
- Industrial equipment such as automated teller machines (ATMs)
- Medical devices such as blood pressure monitors
- Automotive applications such as climate control units, car entertainment systems, car access systems, and mirror and sun-roof control units
"Thanks to smartphones, consumers have come to expect the convenience of touch screens to control a whole host of other devices. With our self-calibrating capacitive touch and proximity switches, NXP is making it straightforward for leading appliance makers, automotive suppliers and other equipment manufacturers to bring touch controls and LCD displays together – with minimal overhead. Through extensive testing, we've also been able to demonstrate the robustness of our solution, even in extreme environmental conditions," said Grahame Cooney, general manager of high-speed interfaces and clock, watches and graphic drivers, NXP Semiconductors. "With world-class LCD drivers, LED controllers, real-time clocks, GPIOs and capacitive touch sensors, NXP offers a comprehensive portfolio of very low power interface solutions that also deliver accuracy, clarity, robustness and reliability over time."
Key features
- Dynamic touch and proximity switch
- Proprietary digital signal processing method
- Adjustable response time
- Continuous over-life self-calibration
- Sensing plate can be placed on a remote location – e.g. 50 cm away
- Lrge temperature operating range (Tamb = -40ºC to 85ºC)
Features specific to PCF8883 and PCA8886
- Adjustable sensitivity; optimized for touch switch or proximity detector
- Wide dynamic input capacitance range: up to 60 pF
- Static capacitance range up to 300 pF
- Wide voltage operating range (VDD = 3 V to 9 V)
- Ideal for battery powered applications (IDD = 3 μA, typical)
Features specific to PCF8885 and PCA8885
- Dynamic touch and proximity sensor with 8 sensor channels
- Support for matrix arrangement of sensors; 28-button single chip
- Cascading of two ICs possible for 64 buttons
- Adjustable sensitivity; ability to cope with up to 6 mm of acrylic glass
- Direct and latching switch modes
- I2C Fast-mode Plus (Fm+) interface with interrupt signaling over two I2C-bus addresses
- Large voltage operating range (VDD = 2.5 V to 5.5 V)
- Low-power battery operation possible (IDD ~ 10 uA); sleep mode (IDD < 100 nA)
Provided by NXP
