Human-machine interface (HMI) for automotive applications has been through several iterations over the last several years. While many vehicles have voice-controlled interfaces, capacitive touch screens are still wildly popular for infotainment systems. 

Capacitive touch sensing is a staple for touch interfaces. To suit the task of controlling these interfaces, Microchip's maXTouch® touchscreen controller ICs for 20-inch displays have been available since December of 2018. 

Last week, Microchip announced another three versions, the MXT1067TD, MXT1189TD and MXT1665TD, that are specifically optimized for nine- to 13-inch automotive touchscreens.

Image from Microchip

The new touchscreen controllers allow engineers to design systems with thick glass or plastic cover lenses that can be controlled even by operators wearing gloves. The devices will prevent water drops of up to 22 mm from being interpreted as “touches.”

Controlling Unwanted Electromagnetic Emissions

Developers of automotive touchscreen systems challenges face challenges in controlling EMI and ESD in the increasingly electronically saturated environment of a modern automobile. To meet this demand, members of Microchip's TD family feature a waveform shaping capability to optimize the performance of the touch controller’s radiated emissions through an EMI optimization tool.

Through this tool, OEMs can enter the RF limits they require for their unique application transmitted burst waveform used for the touch sensing acquisition and tune the shape of the transmitted burst waveform used for the touch sensing acquisition.

Fanie Duvenhage, Vice President of Microchip’s Human Machine Interface business unit describes the company's approach as prioritizing fast, efficient, simple design, “allowing developers to use the same design environment and product features" for various situations, including lens materials, display sizes, and vehicle models. 

Members of the TD Family

Each of the TD family members can operate even with thick (5mm) glove touches and thick (up to 3mm of plastic) lenses. They all also operate over a range of –40 °C to 105 °C.

The ATMXT1189TD-A. Image from Microchip

The ATMXT1067TD-A is designed for display sizes of up to 10.5 inches.

• Interface: I²C serial interface up to 1 MHz
• Package: TQFP128
• Touch response: > 150 Hz

The ATMXT1189TD-A is best for maximum screen sizes of 13 Inches.

• Interfaces:
  • I²C serial interface up to 1MHz
  • SPI interface up to 8MHz
• Package: LQFP144
• Touch response: > 250 Hz

The ATMXT1665TD-A is meant for display sizes of up to 15 inches.

• Interfaces:
  • I²C serial interface up to 1MHz
  • SPI interface up to 8MHz
• Package: LQFP144
• Touch response: > 250 Hz

Touch Screen Controllers Around the Industry

While touch screen controllers abound, there are relatively few specifically designed for tough automotive environments.

Here are two:

• The CYAT817 Automotive Touch Controller from Cypress Semiconductor is AEC Q100 qualified. Screen sizes of up to 17 inch diagonal can be supported. The device can affect 12C communications at 400 kbps or SPI bit rates of up to 8 Mbps.
• Zinitix’s AT100 can work with screen resolutions of up to 2048 by 2560 pixels. Window thicknesses of approximately 0.5 to 1 mm glass and 0.5 to 1.5 mm plastic can be accommodated. The device is RoHS/Reach compliant.