Capacitive touch controllers increase SNR for EMI qualification

Three maXTouch touchscreen controllers have been introduced by Microchip, together with optimisation services which address the EMI and EMC challenges of automotive touchscreens.

The MXT1067TD, MXT1189TD and MXT1665TDTD family of touch controllers have a differential mutual signal acquisition method that significantly increases the signal-to-noise ratio (SNR), explains Microchip. This allows the use of very thick glass or plastic cover lenses and multi-finger thick gloved touch support up to the equivalent of 4.5mm polymethyl methacrylate (PMMA).

The touchscreen controllers are cost-optimised for nine- to 13-inch automotive touchscreens and are complemented by the recently introduced MXT449TD, MXT641TD, MXT2113TD and MXT2912TD devices supporting up to 20-inch touchscreens. Each addresses aspects of functional safety features and is designed in accordance with the Automotive SPICE Level 3 capability and ISO 26262 automotive safety integrity level (ASIL) B requirements.

The latest and existing controllers in the TD family have a waveform shaping capability to optimise the performance of the touch controller’s radiated emissions through an EMI optimisation tool. Developers can enter user-defined RF limits and tune the shape of the transmitted burst waveform used for the touch-sensing acquisition.

Waveform shaping is achieved through firmware parameters derived from the tool and helps designers to position the fundamental burst frequency to work together with other in-vehicle applications, such as the remote keyless entry system. The parameters are added to the maXTouch configuration file, which customises the touch controller performance to the customer design.

This process can save the designer many hours, or even weeks, of expensive EMC test chamber time, explains Microchip, by eliminating experimentation with different configuration settings to achieve the desired EMI/EMC performance.

Target applications for the touchscreen controllers are centre stack displays and navigation systems; they are also suitable for industrial automation and manufacturing stations.

An evaluation kit is available for each of the parts: ATEVK-MXT1067TDAT-A (I2C), ATEVK-MXT1189TDAT-A (I2C), ATEVK-MXT1189TDAT-C (SPI), ATEVK-MXT1665TDAT-A (I2C) and ATEVK-MXT1665TDAT-C (SPI). Each kit includes a PCB with the maXTouch touchscreen controller, a touch sensor on a clear glass lens, the flat printed circuit (FPC) to connect to the sensor and a bridge PCB to connect the kit to the host computer via USB, as well as cables, software and documentation. All parts are compatible with maXTouch Studio, a full software development environment to support the evaluation of maXTouch touchscreen controllers.

The maXTouch EMI optimisation service will be made available as part of the system support provided by one of Microchip’s worldwide application design centres.

The MXT1067TD, MXT1189TD and MXT1665TD devices are available now in sampling and volume quantities in TQFP128 (MXT1067TD only) and LQFP144 packages.

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