Low EMI/EMC Emission Switching Converter Eases ADAS Designs

June 26, 2018 // By Tony Armstrong, Analog Devices
Advanced Driver Assistance Systems (ADAS) usually facilitate safe driving and can provide the driver with an alert if the system detects risks from surrounding objects such as errant pedestrians, cyclists or even other vehicles on an unsafe trajectory. It is the increasing focus of consumers on safety, demands for comfort while driving and the continued increase of government safety regulations that are main growth drivers of ADAS in automobiles for the latter half of this decade.

This growth does not come without challenges for the industry, which include pricing pressure, inflation, complexity and difficulty in testing these systems. Moreover, it should come as no surprise that the European automotive industry is one of the most innovative automotive market, and as such, it has seen major market penetration and adoption of ADAS from its customers. Nevertheless, both the American and Japanese auto makers are not far behind. The ultimate goal is an autonomous driving machine without the need for a human being behind the wheel!

System Challenges

Generally speaking, an ADAS system incorporates some kind of microprocessor to gather all of the input from the numerous sensors within the vehicle and then process them so that they can be easily presented to the driver in a way that it can be easily understood. Moreover, these systems are usually powered directly from the vehicles main battery that is a nominal 9V to 18V in a car, but could be as high as 42V due to voltage transients within the system, and as low as 3.4V during a cold-crank condition. Therefore, any DC/DC converters within these systems must be able to handle the wide input voltage range of 3.4V to 42V, at a minimum. Furthermore, many dual battery systems, such as those commonly found in trucks, require an even broader input range, pushing the upper limit as high as 65V. As a result, some ADAS manufacturers design their systems to cover a 3.4V to 65V input range so that they can be used in either cars or trucks; while gaining economies of scale during the manufacturing process.

Many ADAS systems use a 5V and 3.3V rail to power their various analog and digital IC content; correspondingly, the manufacturers of such systems prefer to use a single converter to address both the single and double battery configurations simultaneously. Furthermore, the system is usually mounted in a part of the vehicle which is both space and thermally constrained, thereby limiting the heat sinking available for cooling purposes. While it is commonplace to use a high voltage DC/DC converter to generate a 5V and 3.3V rail directly from the battery, in today’s ADAS systems a switching regulator must also switch at 2MHz, or greater, rather than the historical switching frequency of sub-500kHz. The key driving force behind this change is the need for smaller solution footprints while also staying above the AM frequency band to avoid any potential interference.

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