Networked and connected home appliances allow users and manufacturers to communicate with them through the internet. For example, the user of a kitchen oven may look up a new recipe online, or a manufacturer could perform remote diagnostics or over-the-air firmware updates. Displays and touch sensors are crucial for allowing this functionality in modern appliances. Microchip Technology is adding two new members to its family of IEC/UL 60730 Class B certified touchscreen controllers. The new MXT448UD-HA and MXT640UD-HA increase the Class B portfolio of devices beyond 10", therefore, offering dedicated solutions for larger screen sizes as well as scalability to customers.
As well as Class B, these new devices are also compliant with the IEC61000-4-6 Class A specification for conducted noise immunity up to 10Vrms (level three for industrial use). This allows products with a touch screen interface to operate in harsh factory environments where electromagnetic interference may be caused by conveyor belts, power rails or assembly machinery. Manufacturers of home appliances will profit from an increased reliability and production yield. This is a large improvement for consumers utilising unprotected touchscreens on an oven or washing machine that could result in concern for false or missed touches caused by electromagnetic interference from unshielded power transmission, electric motors, and neighbouring electrical equipment.
These new touchscreen controllers are also provided with two serial interfaces (SPI and I²C) that work simultaneously providing redundancy in a design through the combination of safety features, such as individual communication between the touchscreen controller to the host MPU in addition to a safety MCU. Touch events are provided to both processors at the same time. This unique architecture reduces time to market and decreases development cost by enabling all safety-critical firmware to be produced on a dedicated safety-certified MCU (with mandatory source code review by an IEC/UL test lab) separate from the main processor running the appliance’s GUI.
“As products add more controls via a touch screen, the interface must work reliably to both satisfy and protect users,” said Clayton Pillion, director of Microchip’s human-machine interface business unit. “maXTouch technology delivers outstanding noise immunity performance allowing for safe and robust operation throughout its lifetime. We have worked closely with customers to deliver the first functional safety touch controller families and are seeing high adoption where noise immunity is critical to a successful product.”
In addition to the IEC compliances, the family supports an operating temperature up to 105C, a principal demand for cooktops and ovens where the HMI system is near heating elements.