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ADAS Demand Multi-Rail DC/DC Converters

Technology News |
By Christoph Hammerschmidt

ADAS typically provide dynamic features such as adaptive cruise control, blind spot detection, lane departure warning, drowsiness monitoring, night vision and even more. As a result, it is the increasing focus of consumers on safety, demands for comfort while driving and the continued increase of government safety regulations that are fueling the growth of ADAs in automobiles.

At the heart of most ADAS systems is some kind of microprocessor to process all the input from the various sensors within the vehicle and to then process it so that it can be easily presented to the driver in a way that it can be easily seen and understood. Moreover, these systems are usually powered directly from the vehicles main battery that is a nominal 9V to 18V, but could be as high as 42V due to voltage transients within the system, and as low as 3.5V during a cold-crank condition. Thus, it is clear that any DC/DC converter to be used must be able to handle a broad input voltage range of 3.5V to 42V.

Many ADAS systems will need a 5V and 3.3V rail to power its various analog and digital IC content; however, it will be the processor I/O and Core voltages that will be in the sub-2V realm. Furthermore, there are space and thermal considerations that must also be taken into account. While it is commonplace to use a high voltage DC/DC converter for a 5V and 3.3V rail, utilizing this kind of converter for sub-2V rails is not always practical due to the solutions size of using multiple single output converters and the potential thermal constraints. A more a suitable solution would be to use a single DC/DC converter with multiple outputs.

Multi-Rail DC/DC Converter

It was because of these constraints that Linear Technology developed its 4-output monolithic synchronous buck converter, the LT8602. Its 3V to 42V input voltage range makes it ideal for automotive applications, including ADAS, which must regulate through cold-crank and stop-start scenarios with minimum input voltages as low as 3V and load dump transients in excess of 40V.


As can be seen in Figure 1, its quad channel design combines two high voltage 2.5A and 1.5A channels with two lower voltage 1.8A channels to deliver four independent outputs, delivering voltages as low as 0.8V, enabling it to drive the lowest voltage microprocessor cores currently available. Its synchronous rectification topology delivers up to 94% efficiency while Burst Mode operation keeps quiescent current under 30µA (all channels on) in no-load standby conditions making it ideal for always-on systems.

Figure 1.  LT8602 Schematic Delivering 5V, 3.3V, 1.8V & 1.2V Outputs

The LT8602’s switching frequency can be programmed from 250kHz to 2MHz and synchronized throughout this range. Its 60ns minimum on-time enables 16VIN to 2.0VOUT step-down conversions on the high voltage channels with a 2MHz switching frequency. As the high voltage VOUT2 channel feeds the two low voltage channels (VOUT3 and VOUT4), these can deliver outputs as low as 0.8V while also switching at 2MHz, offering a very compact (~25mm x 25mm) quad output solution.

About the author:

Tony Armstrong is Director of Product Marketing, Power Products, at Linear Technology Corporation. He can be reached via tarmstrong@linear.com

 


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