Capacitive touch controllers quicken automotive EMI qualification
The TD series of touch controllers feature a new differential mutual signal acquisition method that increases the Signal-to-Noise Ratio (SNR). This technique permits the use of thick glass or plastic cover lenses and multi-finger thick gloved touch support up to the equivalent of 4.5 mm polymethyl methacrylate (PMMA).
The MXT1067TD, MXT1189TD and MXT1665TD devices have cost-optimised variants for 9- to 13-inch automotive touchscreens. Each device is designed in accordance with the Automotive SPICE Level 3 capability and ISO 26262 ASIL B requirements.
All TD family devices have a waveform shaping capability to optimise the performance of the touch controller’s radiated emissions through an EMI optimisation tool. The tool allows developers to 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 resulting parameters are then simply added to the maXTouch configuration file, which customises the touch controller performance to the individual customer design. The process can save the designer many hours, or even weeks, of expensive EMC test chamber time by eliminating experimentation with different configuration settings to achieve the desired EMI/EMC performance.
An evaluation kit is available for each of the parts in the new maXTouch touchscreen controller family. Kit numbers are 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 Printed Circuit Board (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 also compatible with maXTouch Studio.
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