With operating voltages for a variety of high-speed systems settling for the moment in the 1- to 3.3-volt region and thus somewhat of a design constant, the name of the game is boosting total output current to the highest levels, followed closely by transient response and packaging. Indeed, today's designers speak largely in terms of current delivery, current density, di/dt response and synchronous rectification.

Thermal considerations largely drive packaging advances, with more open-frame designs on the scene to address cost issues as users up their demand for price-competitive converters that maintain the full specified output at the highest temperatures possible with no derating, especially for telecom applications. Vendors have responded with a spate of products, many involving bricks-rectangular modules in industry-standard package sizes and pinouts-and largely but not universally identified as an isolated power source. Entries range from newly arriving one-eighth brick converters to quarter bricks with up to 50-amp capability, to half bricks that deliver 80 A.

A snapshot of the most recent activity focused on high current and packaging reveals two arriving dc/dc converters, the first officially termed an eighth brick, that herald what some deem a new paradigm for power system design. With eighth bricks on many companies' road maps but still in limbo as manufacturers contemplate a de facto standard, Vicor's 75-watt PowerStick is considered the first U.S. entry in that direction.

Datel Corp. (Mansfield, Mass.) has just announced that its ULE series is a short step away from sampling. The isolated single-output ULE (unipolar, low-cost eighth brick), positioned amid the company's recent USQ quarter-brick series, will provide about 50 W at 1.2 to 15 V from nominal 12-, 24- or 48-V inputs. That implies operating currents approaching 20 A.

"Pinout compatibility was most significant to this design," said Bob Leonard, product-marketing manager. "The approach we took is to be able to drop it into a quarter-brick pinout," he said of the 2.28 x 0.78-inch package.

"The eighth brick opens the door to many system options," Leonard said. "You could take two of these and make a quarter brick with two isolated outputs, or a quad half brick-all with independent control loops." The company said pricing for the ULE is intended to come in at under $50.

At the same time, di/dt Inc. (Carlsbad, Calif.) might be the company to bring an eighth-brick design to market first, in at least limited quantities. The as-yet-unnamed series, which will be designed to deliver upwards of 50 W, is also likely to adopt the quarter-brick pinout, di/dt said.

At least 20 items for patent consideration resulted from that technology set, said Bob Cantrell, vice president of marketing and sales. A large part of the work addresses thermal considerations.

The implied endpoint for these eighth-brick-style designs is converters that deliver full output at ambient temperatures encountered in telecom applications: operation at 70 degrees C and little or no external cooling-an often-cited goal by dc/dc makers.

Meanwhile, dc/dc activity is presently most intense with quarter bricks (footprint of approximately 2.3 x 1.45 inches) and half bricks, where the competition has largely become a fast-moving race to deliver the most current and maintain full output at higher operating temperatures. More converters utilize synchronous-rectifier topology, implying an efficiency approaching 90 percent or so.

In quarter bricks, the EXQ50 series of synchronous-rectified, open-frame modules from Artesyn Technologies (Eden Prairie, Minn.), just 0.4 inch high, deliver 50 W at 1.8, 2.5, 3.3 or 5 V and a peak current capability of up to 20 A (at up to 2.5 V). It's specified for operation over an ambient temperature range of -40 degrees C to 90 degrees C.

The company bills the EXQ50 as delivering more usable power under low-airflow or natural-convection conditions than competing converters. Artesyn earlier released the EXQ60, a dual-output quarter brick delivering a total of 60 W and a maximum output current of 15 A at 3.3 V and 12 A at 5 V.

Another low-voltage, high-current product is di/dt's QL48T30/S30, which can deliver 30 A at 0.8 V. Meanwhile, Ontario-based Celestica Inc. has just released the QHS40 series of quarter bricks, which delivers 40 A at 1.2, 1.8 or 2.5 V. Efficiency is 87 percent at 1.8 V. Pricing starts at $75 each on an annual purchase of 1,000 units.

SynQor (Hudson, Mass.), perhaps the first company widely associated with synchronous rectification, has released its PowerQor QTA Tera series, delivering up to 40 A at 2.5 down to 1.2 V from a nominal 48-V input, and 35 A at 3.3 V, without the need for a heat sink. These converters deliver their full output at 55 degrees C (with 300-LFM airflow). The price is $96 each in quantities of 1,000.

Another new quarter-brick arrival, Datel's aforementioned 100-W single-output USQ series, is available in 1.2- through 18-V versions in 65 models delivering up to 20, 30 or 40 A at the lower voltages from a 24- or 48-V input. It's touted for breadth of current and voltage input/voltage output at a good price ($65 in OEM quantities), while offering output-current capability, power and performance typically expected of half bricks.

Transient response is 200 microseconds to plus/minus 1 percent for a 50 to 75 percent load step. Line and load regulation is plus/minus 0.05 percent maximum, noise is 50 mV peak to peak and the converter delivers fully rated output power from -40 degrees C to 60 degrees C without a heat sink. With a heat sink, it operates over the extended range, to 100 degrees C. Mean time between failures is greater than 2.5 million hours.

Mastering current-density and output-current issues means cutting I2R power losses to improve efficiency and minimize thermal issues. Broadband Telcom Power (Santa Ana, Calif.) utilized its flat-matrix transformer technology in delivering its HQ series of synchronous-rectified quarter-brick converters. Delivering up to 50 A at 1.8 V, 45 A at 2.5 V and 40 A at 3.3 V from a nominal 48-V input, the HQ is being billed as the highest-current quarter brick in the industry. The company's multiple-core, single-winding technology essentially divides the output current among the cores, thus reducing total I2R losses by up to a factor of 4.

In addition, the secondary windings of the converter's 1:1 transformers are bonded to the inside of the cores to ease heat transfer to the outside environment. The cores are designed with thin walls to reduce eddy losses and to provide a short thermal path. The trade-off of the flat-transformer technology is a slightly greater converter footprint but a lower profile. These modules are priced at $95 each in lots of 1,000. Broadband Telcom Power has yet higher-current quarter bricks on its road map.

The same high-output-current issues permeate half bricks (with a footprint of approximately 2.3 x 2.4 inches). Artesyn, Synqor and Ericsson Microelectronics (Richardson, Texas) have all been marketing low-voltage, high-current (60-A) product lines. In December, Tyco Electronics Power Systems (Dallas) released its JRW-070 series of 1- to 12-V low-profile (0.38-inch) converters, which can deliver up to 70 A in a half-brick, single-board package. The JRW070 achieves an efficiency of 91 percent at 3.3 V output. It's priced at $117 each in quantities of 1,000.

Tyco's JHW133W, meanwhile, is the first in a family of dual-output dc/dc converters to deliver two regulated 16-A outputs at 5/3.3 V or 3.3/2.5 V for broadband, wireless and optical networking markets.

80-A half brick
For its part, Astec Power (Carlsbad, Calif.) has announced its ALH80/AEH80, a three-version series (1.2, 1.5 and 1.8 V output from a nominal 48-V input), billing it as the industry's first 80-A half brick. It's available in an open-face version (ALH80) or with an attached heat sink adapter plate (AEH80), both intended for a range of applications-from wireless basestations, hubs and routers to instrumentation. It's priced from $130 each in lots of 1,000.

User interest in the larger bricks has waned as the trend continues to smaller and distributed low-power and N+1 type architectures. The three-quarter brick (2.45 x 3.45-inch footprint), for example-such as the 100-A, 150-W TXS that Power-One (Camarillo, Calif.) released last year-is one of the few available for distributed power, which is expanding on its original definition as a concentrated, low-power architecture. On the other hand, there is a bit more interest in full bricks (4.6 x 2.5-inch footprint), and a few may arrive this year for service in the 500-W arena.

Broadband Telcom Power first released a 960-W, 185-A module in 2000 using its flat-transformer technology in a form slightly larger than a full brick. In a twist, the converter was designed as a single-unit, high-reliability alternative to a shared-current, multiple-module scheme.

Apart from the various PC and desktop power architectures that have come to depend on bricks, so-called nonstandard-size modules are competing well, and many dc/dc brick makers sport such products. Even the nonbricks are evolving to embrace several "standard" sizes and pinouts. They're often marketed as low-cost alternatives for applications where the full output of a brick isn't needed.

New arrivals include the UHE series of 20-A modules from Datel and the CostCutter series (2.76 x 3.25 x 0.75 inches) from Astrodyne (Taunton, Mass.), which has expanded to 60 W (derated after 71 degrees C, for 590 LFM). Astrodyne's FDC60, providing 3.3 to 15 V in single and dual outputs, comes in more than 20 versions.

Company Contacts

Artesyn Technologies
Call (952) 392-6538
www.artesyn.com
EETInfo No. 620

Astec Power
Call (978) 645-4503
www.astec.com
EETInfo No. 621

Astrodyne
Call (508) 823-8080
www.astrodyne.com
EETInfo No. 622

Broadband Telcom Power Inc.
Call (714) 259-4888
www.btcpower.com
EETInfo No. 623

Celestica Inc.
Call (416) 386-7700
www.celestica.com
EETInfo No. 624

Datel Corp.
Call (508) 339-3000
www.datel.com
EETInfo No. 625

di/dt Inc.
Call (760) 795-3500
www.didt.com
EETInfo No. 626

Ericsson Microelectronics
Call (877) 374-2642
www.ericsson.com/microe/
EETInfo No. 627

Power-One
Call (805) 987-8741
www.power-one.com
EETInfo No. 628

SynQor
Call (888) 567-9596
www.synqor.com
EETInfo No. 629

Tyco Electronics Power Systems
Call (800) 526-7819
www.power.tycoelectronics.com
EETInfo No. 630

Vicor
Call (978) 470-2900
www.vicr.com
EETInfo No. 631