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Multi-channel synchronous buck converters for car apps

Posted: 24 Nov 2015 ?? ?Print Version ?Bookmark and Share

Keywords:power ICs? power management? Infotainment systems? capacitors? LT8602?

As automobiles continue to incorporate a higher density of electronic systems to enhance safety, comfort, efficiency and performance, it is not surprising that they need both smaller and higher performance power conversion solutions. These new multi-channel power management solutions need to deliver up to four independent power rails usually to power VCORE, VI/O, VMEM required for microprocessors and generally a fourth 5V rail to power a CAN transceiver.

According to Strategy Analytics, "The demand for enabling semiconductor devices is expected to grow at a compound average annual growth rate (CAGR) of five per cent over the next seven years, with the total market worth over $41 billion by 2021, compared to $30 billion in 2014." They also identified that demand for microcontroller and power semiconductors will drive over 40 per cent of revenues.

Strategy Analytics provides a very quantitative description of forecasting the growth of electronics content in automobiles, but more interesting is the prevalent role that power ICs play in this growth. These new power ICs must provide:
???Multiple voltage rails from a single power management IC
???Robust performance across a wide range of voltages, including cold-crank and stop-start scenarios from ???Outputs ranging from 5V down to less than 1V
???Ultra low electromagnetic interference (EMI) emissions
???The highest efficiency possible to both minimise thermal issues and optimise battery run-time
???Ultra low quiescent current (infotainment systems to stay engaged without draining the vehicles battery when its engine (alternator) is not running.
???The smallest solution footprints, often requiring multiple voltage rails to minimise space required for power conversion circuits
???Switching frequencies of 2MHz or greater to keep the switching noise out of the AM Radio band and to keep solution footprints very small

The goal of the increased performance levels of power ICs is to allow the design of increasingly numerous and complex and electronic systems found within automobiles. Specific applications which are fueling the growth for electronic content in cars are found in every aspect of the vehicle. For example, new safety systems including lane monitoring, adaptive safety control, automatic turning and dimming headlights. Infotainment systems (telematics) which continue to evolve and pack more functionality into an already tight space must support an ever growing number of cloud based applications. Advanced engine management systems with the implementation of stop/start systems, electronically controlled transmissions and engine control. Drive train and chassis management aimed at simultaneously improving performance, safety and comfort. A few years ago these systems were only found in "high-end" luxury cars but now they are commonplace in automobiles from every manufacturer, further accelerating the automotive power IC growth.

Smaller power conversion circuits
There are a few ways to make power conversion circuits smaller. In general, the largest components in a circuit is not the power IC, but the external inductor and capacitors. By increasing the switching frequency of the power IC from 400kHz to 2MHz, the size of these externals can be dramatically reduced. However, in order to do this effectively, the power IC must be capable of delivering high efficiency at these higher frequencies, which historically has not been feasible. Nevertheless, using new process and design techniques, synchronous power ICs have recently been developed that can deliver efficiencies in excess of 90% while switching at 2MHz. The high efficiency operation minimises power loss, eliminating the need for heat sinks. It also has the added benefit of keeping switching noise out of the AM frequency band which is critical in many noise sensitive electronic systems.

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