It's Time to Standardize Point-of-Load Converters

Aug 1, 2003 12:00 PM
Ashok Bindra, Editor

Through the decades, the pc-board landscape has changed dramatically. With the proliferation of low-voltage, high-current microprocessors/DSPs and high-voltage analog and power devices on a single card, the number of different voltages encountered on a single board has mushroomed. This has forced designers to refine the popular distributed power architecture (DPA) into a scheme with intermediate bus voltage, and convert this bus voltage into the desired voltage at the point-of-load (POL) using dc-dc converters. In effect, a two-stage power conversion — the first stage converts ac to high-voltage dc and the second stage converts this high-voltage dc to intermediate bus voltage — scheme is becoming popular with POL converters delivering the required regulated voltage.

It's not surprising, then, to see more semiconductor players and module makers entering this arena. To get the maximum out of such an architecture, some are modifying the traditional approach to propose their own versions of the conventional DPA. Others have come up with an optimum number for this intermediate bus. Meanwhile, POL converters are manufactured in a variety of shapes, forms, and pin outs.

Because there's no single choice for the second level distribution bus, which depends on factors such as cost, efficiency, and size, dc-dc makers are designing POL converters with several input voltage ranges. Although many favor 12V as the right value for the intermediate bus, pundits have argued that 6V to 8V is an optimum range as far as efficiency is concerned. Taking several factors into consideration, International Rectifier is betting on 8V as the appropriate value for this intermediate bus. Depending on applications, power supply manufacturer Datel is touting a variety of optimum intermediate voltages.

Traditionally, bus converters reducing the high front-end voltage to a low intermediate value have been isolated bricks, as well as some semiconductor chipsets for embedded or in-house solutions. They go by different names, and their outputs can be fully regulated, semi-regulated, or unregulated. By far, POL converters at the load have been nonisolated. Recently, that tradition was altered with Vicor's factorized power architecture (FPA). It comprises building blocks like pre-regulator module (PRM) and voltage transformation module (VTM). Based on the output voltage, load current, available space and system cost requirements, these multichip modules (MCMs) can be configured in a variety of ways. Interestingly, unlike conventional bricks, PRMs provide nonisolated and regulated output, while VTMs deliver isolated and regulated output to the load.

So, it's not surprising to see POL converters in a multitude of forms, functionalities, and footprints. Some handle input ranges between 5V and 12V, others handle narrow input ranges, and many handle point-to-point conversions. They're available in myriad packages, and the number of proprietary POL suppliers continues to increase as the intermediate bus architecture gains momentum.

Think of the user who is confronted with this vast array of products, yet no standard exists. Each one brags its own solution is the best. Although Artesyn Technologies and Astec Power recently inked a second-source licensing deal with Texas Instruments for a specific TI POL family, it's a drop in the bucket. To make life simpler and to propel this architecture, suppliers must come together and initiate a standardization process. It's about time, don't you think?

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