Capacitive touchscreen controller is at home in harsh, noisy environments

Functional safety-certified capacitive maXTouch touchscreen controllers from Microchip now include the MXT448UD-HA and MXT640UD-HA models, designed to address screen sizes beyond 10 inches.

Networked and connected home appliances enable both users and manufacturers to communicate with them via the internet. This can be a user of a kitchen oven looking up a recipe online or a manufacturer performing remote diagnostics or over-the-air firmware updates. Displays and touch sensors are essential for enabling this functionality in modern appliances and now Microchip Technology has extended the Class B portfolio of touchscreen controllers with two models for larger screen sizes, providing scalability.

The two new members of the IEC/UL 60730 Class B certified touchscreen controller family comply with the IEC61000-4-6 Class A specification for conducted noise immunity up to 10 Vrms (level three for industrial use). This enables products with a touchscreen interface to function in very harsh factory environments where EMI can be caused by conveyer belts, power rails or assembly machinery. In home appliances, manufacturers will benefit from an increased reliability and production yield, says Microchip, rather than risk consumers using unprotected touchscreens on an oven or washing machine that may result in false or missed touches due to EMI from unshielded power transmission, electric motors and neighbouring electrical equipment.

The MXT448UD-HA and MXT640UD-HA touchscreen controllers come with two serial interfaces (SPI and I²C) that operate simultaneously allowing redundancy in a design through the integration of safety features, such as individual communication between the touchscreen controller to the host microprocessor in addition to a safety microcontroller. Touch events are provided to both processors at the same time. This architecture shortens time to market and reduces development cost by allowing all safety-critical firmware to be developed on a dedicated safety-certified microcontroller (with mandatory source code review by an IEC/UL test lab) separate from the main processor running the appliance’s graphical user interface (GUI).

According to 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 MXT448UD-HA and MXT640UD-HA family supports an operating temperature up to 105 degrees C, which is a key requirement for cooktops and ovens where the human machine interface (HMI) system is near heating elements.

Microchip offers software to supplement the controllers, including maXTouch Studio (development tool) and maXTouch Analyzer (production end-of-line test/inspection tool).

The general-purpose ATEVK-MXT640UD-A evaluation kit (EVK) is available. The home appliance functional safety version of this evaluation kit is available on request.

The ATMXT448UD-CCUHA1 and ATMXT640UD-CCUHA1 are available in volume production now.

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