Electronic Design

Power> DC-DC Converters

Distributed Power Architectures Battle While POLs Fight Over Standards

During 2003, the focus in dc-dc converters shifted from the actual converters to the distributed-power architectures using these devices. Sure, many announcements heralded better dc-dc converter performance. But even greater attention was paid to architectural developments that promise to bolster performance as well as reduce cost and space requirements for power systems.

Several vendors expressed their support for the intermediate voltage bus architecture (IBA) by introducing the necessary bus converters. Even the IC manufacturers got in the game by offering bus converter chips and chip sets. Simultaneously, a mounting number of nonisolated point-of-load converters (POLs) debuted. Many of these devices are no doubt aimed at IBA applications, which rely more on nonisolated point-of-load converters than on bricks.

Meanwhile, Vicor unveiled the Factorized Power Architecture (FPA) and a related set of BGA-style power components. The performance specifications FPA promised were outstanding. But its approach of distributing a pre-regulated but nonisolated high-voltage dc bus to a series of isolated POLs generated wonder and confusion.

By now, some of that confusion may have dissipated since the company openly discussed the new approach's rationale and principles of operation. Vicor also removed a potential hurdle to commercializing FPA by licensing it to Celestica. As the electronics industry continues to recover, the battle between FPA and IBA should heat up.

A general interest in nonisolated POLs has led to a proliferation of these devices. Many hundreds of models have emerged to provide countless combinations of voltages, currents, and package types. The glut of part numbers has many clamoring for standardization.

In response, some vendors have adopted the footprint and pinout of Tyco's Austin series. Others have opted for alternatives like Texas Instruments' POL alliance. Meanwhile, Datel has advocated the eighth brick as a POL standard.

Power-supply vendors will also try to resolve how much of the dc-dc converter should be digital. Microcontrollers are now being used to add features and enhance performance for otherwise analog designs. But some vendors want to push digital further, using it to manage the control loop and create a more flexible converter design.

See associated figures 1 and 2

TOP TEN

  • MCUs WILL BEGIN TO EXPAND THE FUNCTIONALITY of nonisolated point-of-load dc-dc converters. For example, Artesyn Technologies plans to introduce "smart" POLs that incorporate an on-board microcontroller for the purpose of storing relevant data. For example, test information such as a unit's serial number may be stored in the POL.
  • SOME VENDORS WILL EXPLOIT THE POWER OF THE MCU to improve converter performance. Datel, for one, will embed microcontrollers to create POLs that provide adjustable output voltages without sacrificing converter performance. Although existing POLs can offer a wide output voltage range via a trim adjustment, these devices are typically optimized only at their natural output voltage. At other output voltages, the POLs' efficiency, step response, and stability may be compromised. Datel will overcome these deficiencies by using on-board MCUs to select the clock frequency and compensation scheme based on the programmed output voltage.
  • POWER-SUPPLY VENDORS WILL CONTINUE to enhance their isolated and nonisolated dc-dc converters by adding features to manage sequencing, tracking, margining, and monitoring of multiple supply voltages. Such converters will replace external controller ICs and discrete MOSFETs that often manage the ramping up and down of supplies. For example, Power-One will integrate the needed control functions into its isolated bricks and converters so the two work together to perform the desired operations.
  • EXPECT THE CURRENT DENSITY OF NONISOLATED POLs to increase by a factor of two or more. For example, in the first half of this year, one vendor plans to offer a 30-A POL in the Austin-style footprint, which currently offers 15 A of output. Meanwhile, power-supply vendors will continue to offer POLs with higher current ratings. If recently introduced nonisolated converters boast 40 A of output, those introduced in the coming year may promise 50 A or more from a single package.
  • TRANSIENT RESPONSE IS ON THE RISE for POL converters. POLs with 200 A/µs or better are already appearing—a tremendous increase over the 1-A/µs response of some older nonisolated converters. Such performance will blur the lines separating general-purpose POLs from CPU-dedicated voltage regulator modules (VRMs).
  • DC-DC CONVERTERS WILL CONTINUE to increase in power density, deliver higher levels of current, and generate lower output voltages. The Power Sources Manufacturers Association's recently released technology roadmap provides five-year forecasts for these parameters. For isolated "brick" converters in the 100-W range, the 75-W/in.3 power density of existing converters is expected to rise to 100 W/in.3 in 2008. Over the same time period, the 30- to 60-A output capabilities of existing converters will climb to 45 to 100 A. Along with these gains, efficiencies will jump from the 85% to 93% range to a 90% to 95% range. The better efficiencies are impressive considering the dropping supply voltages. While 1.2- to 3.3-V outputs are ubiquitous now, dc-dc converters with outputs as low as 0.8 V will be common in five years.
  • THE PSMA'S FIVE-YEAR ROADMAP also predicts significant reductions in 100-W converter cost accompanied by gains in converter reliability. Costs now estimated to be at $0.40 to $0.60/W are expected to fall into the $0.20 to $0.45/W range. Meanwhile, MTBFs, which are now around 1 to 2 Mh, will rise to 4 Mh.
  • ALTHOUGH MOST BRICKS NOW OFFER A NOMINAL 48-V input with a 2:1 input voltage range of 36 to 72 V, a few now come with a 4:1 input voltage range of 20 to 80 V. Expect to see more brick manufacturers offering the wider (4:1) input voltage range to accommodate the popular 24-V bus found in GSM applications
  • VENERABLE BRICK PACKAGES will continue to show their staying power in the coming year as power-supply vendors exploit these packages in emerging applications. Bus converters—isolated but unregulated dc-dc converters optimized for intermediate voltage bus architectures (IBAs)—are one example. Last year, a few were introduced in the quarter-brick package. More are likely to appear this year. Similarly, half bricks were developed for Power over Ethernet (PoE) applications, where they generate a 48-V output (52.5 V actually, to compensate voltage drops over the LAN cable) that's isolated from the 48-V system supply. Look for more of these types of products aimed at PoE. Also expect to see the eighth-brick package make inroads into the world of nonisolated converters. Other vendors are expected to join Datel in offering a nonisolated eighth brick.
  • LAST YEAR SAW A FEW INTRODUCTIONS of nonisolated POLs in IC-style packages like the LGA and the BGA. These devices, which are essentially multichip modules, offer current levels of 15 A or more. That capability distinguishes them from the increasingly powerful monolithic dc-dc converters, which now deliver as much as 9 A. The performance gap separating monolithic dc-dc converters and multichip module dc-dc converters may narrow in the coming year. Yet the modules will face growing competition from the monolithic parts as more components are introduced. Newer monolithic dc-dc converters will offer wider input voltage ranges and other performance-enhancing features.
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