Versatile automotive touchscreen controller includes functional safety support

Multiple communication options, ISO 26262 functional safety support and flexible RF emission control are offered in the maXTouch touchscreen controller, says Microchip Technology.

According to the company, it allows automotive designers to satisfy various aspect ratios for touch displays in cars and, in response to requests by OEMs,  includes additional functional safety support.

The MXT1296M1T can reconfigure its driving and receiving touch channels to match the exact screen format, from 1:1 to 5:1 aspect ratio, i.e., including the popular 8:3 automotive aspect ratio. This allows the customer to efficiently use the number of touch channels available, without needing a larger, more expensive touch controller. Customers can save additional development and validation time, as well as resources, by reusing a common PCB design to support different touch sensor aspect ratios. The MXT1296M1T is believed to be an industry first in that it enables the sensor channel reconfiguration by parameters. Settings do not require firmware modification, which reduced the design risk and also the time to market.

Clayton Pillion director of the human machine interface (HMI) business unit at Microchip Technology, observed: “Products with enhanced diagnostic features are a significant advantage to customers who are designing with unique features and increasing ISO 26262 functional safety requirements in mind”.

The MXT1296M1T maXTouch touchscreen controller offers two communication interfaces operating simultaneously, which allow a bridgeless connection to the back channel of the LVDS video link for touch information and a connection to a local microcontroller. The bridgeless topology reduces touch latency to improve the user experience. It also guarantees compatibility with the maXTouch software driver, available for all major automotive operating systems, including Linux, Android and QNX. 

When connected to an appropriate local microcontroller, the second interface offers a number of benefits. Firstly, it offers a redundancy link to the head unit through a CAN bus or 10BASE-T1S automotive Ethernet link for increased functional safety at the system level. There is also local access and control of the maXTouch touchscreen controller’s features, for example, capacitive keys report, live touch sensor diagnostics and raw data for external and custom post-processing. 

Finally, there is over the air (OTA) and secure firmware update capability using Microchip’s TrustAnchor100 companion chip

The MXT1296M1T embeds various functional safety features to constantly check the integrity of the touch controller operation, as well as that of the connected touch sensors. The failure modes effects and diagnostic analysis (FMEDA) and functional safety manual support the customer in designing, building and certifying a system for Automotive Safety Integrity Level B (ASIL-B) applications to the ISO 26262 standard.

The MXT1296M1T allows for high resolution transmit waveform control to lower RF emissions and avoid interference with the car radio or RFID systems. As screen sizes  increase in cars, RF emissions generated by the projected capacitive touch technology are growing. (Emission limits vary in amplitude, frequency and bandwidth for each major car manufacturer.) The MXT1296M1T uses a dedicated on-chip 64-level DAC to accurately shape the waveform of the transmitting lines. As a result, designers can precisely control the frequency response and optimise the harmonic emissions to meet specific OEM-defined limits.

The MXT1296M1T configuration and tuning is supported by the latest release of maXTouch Studio integrated development environment (IDE). Microchip also offers the 

ATEVK-MXT1296M1T-A evaluation kit for order. This includes a development board with USB bridge, 12.3-inch / 8:3 format / 1.1mm OGS (one glass solution) touch panel, and touch key add-on boards for mutual and self-capacitance. 

There is also the ATMXT1296M1T-I2C-PCB development board for connection to a customer’s touch sensor

The MXT1296M1T is now available in volume production. ISO 26262 FMEDA and Functional Safety Manual will be available for purchase Q1, 2022.

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