Electronic Design

Latest Bricks Lay Foundation For Distributed Power Designs

We're accustomed to hearing Moore's Law quoted regularly to describe progress in the semiconductor world. But could a similar trend be developing among dc-dc converters? Mahmoud Sayani, director of marketing and business development at Celestica Power Systems, has been charting the progress that power-supply manufacturers have been achieving in dc-dc converter development in the various sub-brick formats.

Sayani's look at dc-dc converter performance over the past few years indicates steady improvements in current density and efficiency, accompanied by a continual downsizing of converter packaging. Although it might be premature to characterize any emerging performance trends as a "Moore's Law" for power converters, they could provide insight into the near-term future.

Since the beginning of this year, there have been several announcements of dc-dc converters in an eighth-brick format. Measuring around 2.28 by 0.8 in., the eighth brick is about 40% smaller than the standard quarter brick. With the ability to provide 15 to 20 A at voltages as low as 1 V, the eighth bricks should replace the 2.28- by 1.45-in. quarter bricks in some applications. That's not too surprising as quarter bricks were rated for about the same current level just three years ago.

But today's quarter bricks carry ratings of 40 to 50 A. This makes them candidates for use in applications that formerly required the 2.28- by 2.4-in. half bricks, which specified 30-A ratings three years ago. Meanwhile, half bricks now offer greater than 70-A output. Sayani notes that the available current output has been increasing annually by about 10 A per package. In a related trend, the current level offered in one sub-brick package has become available in the next smaller package every 24 to 36 months, and this pace is accelerating.

Based on these observations, it's possible to project current ratings for next year's dc-dc converters. According to Sayani, we can expect to see general introductions of 100-A half bricks, 60-A quarter bricks, and 30-A eighth bricks in 2003. Meanwhile, the efficiency of dc-dc converters, particularly those with low-voltage outputs, is rising.

For instance, converters with 1.8-V outputs have gone from 84% or lower efficiency two years ago to 88% today. In another year, these same converters should be running with 90% efficiency, says Sayani. But the pressure is on power-supply vendors to do better. Even now, customers demand 90% efficiency at the more challenging 1.2-V output.

Naturally, the gains made in performance and packaging reflect improvements in the available power components and design techniques as well as users' demands for smaller components. But the proliferation of multiple voltages on the pc board is another factor. Power-supply vendors have responded by introducing dual-output half bricks and quarter bricks, and even some triple-output units. Now, eighth bricks add another level of flexibility.

For example, two eighth bricks may supplant a half brick to obtain similar power levels, but with two independently regulated outputs. This tactic permits redundancy, or perhaps an odd voltage combination. Or, a dual quarter brick may be paired with an eighth brick, yielding three voltages in a half-brick footprint.

Toss in vendor-specific variations on the sub-bricks and nonisolated dc-dc converters, and the list of possibilities for distributed power design grows still more. Ultimately, this "more" may be what counts most with designers, whether or not there's a "law" governing the progress in power design.

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