Electronic Design

Auto Power Apps Bristling; Portables Need Complexity

Power-management activity whirls around dc-dc converters. Yet as Linear Technology founder and CTO Robert Dobkin points out, power management could prove an even greater challenge in battery-powered handhelds than on a server system board (see the figure).

Similar thinking led Summit Microelectronics to offer two linkable active points-of-load (POLs)—one four-channel, one six-channel—that implement sequencing, margining, and true differential tracking. In addition, a linking feature allows up to 30 channels of operation. Linking is accomplished by a pin on each POL in the system.

The company's Active DC Output Control (ADOC) Sequencing can be set so each supply begins its startup following a programmed delay after the prior supply completes its transition. ADOC intelligently maintains the POLs' output voltage to ±0.1%, so they're useful in pre-production margining as well as in production systems.

New voltage regulator modules (VRMs) for Intel microprocessors are available from several companies. Texas Instruments provides a power-management integrated IC expressly for Xilinx's Spartan-II/IIE/3 series of field-programmable gate arrays (FPGAs).

The triple-channel device reduces the number of required external components. It integrates two 3-A dc-dc buck controllers with up to 95% efficiency for the core and I/O rails and one 300-mA low-dropout (LDO) regulator VCCAUX rail. Additionally, the chip meets Xilinx's startup profile requirements.

National Semiconductor's LM274x family addresses similar needs for systems with multiple DSPs, FPGAs, and ASICs. National's Webench online design tool lets designers select a power-management product, create and analyze a design, and build custom prototypes that can be delivered within 24 hours.

If consumer products are the next big thing, the automotive business is the grand-daddy of the consumer arena, with its massive consumption of new power devices.

Following Toyota's success with the Prius hybrid, Ford has licensed Toyota's power train. Meanwhile, GM's Sierra/ Silverado hybrid pickups rely on an all-in-one starter/alternator to instantly get the truck going after the regular gas engine shuts itself off during traffic stops and coasting.

In Europe, Mercedes, BMW, and Volkswagen are throwing lots of new features into their biggest luxury cars, where high margins will defray the engineering development costs. Mercedes' S-class vehicle, expected next fall, will have a hybrid drive that comprises a 3.7-liter V6 gas engine rated for 245 hp. Clutches connect two electric motors, one rated for 41 hp, and the other for 34 hp.

The electric motors are actually integrated starter/alternators (ISAs). When automotive engineers re-evaluated the starter motor and the alternator several years ago, they began to understand them not as separate entities, but as candidates for consolidation.

An ISA can keep the battery charged and start the engine, as well as provide the torque needed to get the car rolling again once the stoplight turns green. Meanwhile, the gas engine is engaged in starting and coming up to speed. When the car needs a burst of acceleration, there's the ISA again. An ISA can even fulfill the role of the flywheel or harmonic balancer for the gas engine.

Hybrids aren't the only way to get more mileage out of fossil fuels or to design-in power electronics under the hood. If the goal is 60 miles per gallon, improved diesel engines can achieve 80% of that for half the cost of hybrids. But these aren't the diesels of yesteryear, and they use lots of power electronics.

Diesels operate at a much higher temperature difference than conventional gas engines, making them very efficient. Their only real disadvantage is their emissions, nitrous oxides (NOx) and particulates. Particulates can be handled by filtering. NOx has been more intractable, but diesel engineers are working on new injection and emission control methods.

One method injects multiple pulses of fuel. At the Paris Motor Show last October, Toyota demonstrated piezo injectors in its D-4D concept engine. A piezo injector can perform as many as five injections per cycle. That four-cylinder D-4D develops around 180 hp and 295 ft-lb maximum torque, formerly only possible with a V6 diesel. Toyota says the D-4D delivers NOx and particulate emissions 50% and 80% below Euro IV standards for diesel engines.

Where do power electronics fit in? For one thing, piezoelectric injectors require high-voltage dc-dc converters. Also, diesel doesn't make much sense unless it's turbocharged, where electronics can meter the air to ensure there's enough but not so much as to increase pollution.

Power electronics in active suspensions can help sweeten a car's handling and reduce rollovers. Today's active suspensions are mostly hydraulic, but electronic versions (think of big speaker coils instead of shocks and springs) are on the drawing board. An important advantage of an all-electric active suspension, beyond the fact that it's lighter than an electro-hydraulic hybrid, is a significant simplification of control-loop design.

Electric steering systems use electric motors mounted in the steering rack. Electric power steering, which Honda already uses on its S2000 and Insight models, will become common within three years.

Car makers are desperate to reduce the number of microprocessors scattered through the car, each with its own regulator. In tomorrow's automobiles, car makers would prefer to consolidate the functions of today's myriad processors down to just three: one each for chassis, body, and engine. All would be tied together with a high-speed version of the auto industry's CAN bus. This would clearly call for larger regulators that can respond very quickly to load-current swings.

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