AMP Consortium Steers Future of Digital Power

Several power supply companies are creating a framework that would simplify design-in of digital power modules for OEM applications. Standards will ensure second sourcing and compatibility between different suppliers' modules.

Two of the prevalent power trends in recent years- distributed power and digital power - are the focus of an all-encompassing effort spearheaded by three major power suppliers to ease power system design for OEMs. Last November, Ericsson (now part of Flex Power Modules), CUI, and Murata formed the Architects of Modern Power (AMP) Consortium to establish a framework for digital power modules with common electrical and physical specifications that are readily available through second sourcing.

The AMP Consortium goes beyond previous standardization efforts that were restricted to physical power supply specifications to define the modules' monitoring, control, and communications functions. The AMP Consortium expects to create common configuration files for plug-and-play interoperability to ensure compatibility between each firm's products.

The alliance has defined two sets of standards for digital point-of-load converters. The "microAMP" specification covers supplies rated at 20 to 25A in vertical and horizontal configurations, while the "megaAMP" specification defines requirements for 40 to 50A vertical and horizontal units. For advanced bus DC-DC converters, the "ABC-ebAMP" standard relates to advanced one-eighth size bricks measuring 58.42 x 22.66mm and rated from 264 to 300W. For quarter-brick supplies, measuring 58.42 x 36.83mm and rated 420 to 468W, the Consortium has defined the "ABC-qbAMP" standard.

Consortium founders have wasted no time in bringing products that meet the defined standards to market. Table 1 shows parts currently available meeting the microAMP and megaAMP specifications, while Table 2 shows parts now available to meet the advanced ABC-ebAMP and ABC-qbAMP standards.

Table 1: Digital Point-of-Load Modules. (Source: AMP Consortium)

Table 2: Advanced Bus Converters. (Source: AMP Consortium)

Communications Driving Market

A never-ending increase in data is driving OEMs to build ever-more powerful communications networks that are, in turn, putting added pressure on the power industry for more sophisticated power systems. The Ericsson Mobility Report projects annual IP traffic to reach 7.7 zettabyes (7.7 x 1021) by the end of 2017, up from 2.6 zettabytes in 2012. The trend will be driven by cloud services, video communications, and the much-ballyhooed Internet of Things (IoT). The boom in IP traffic will further stress data network power systems. The growth of advanced processors and FPGAs are expected to further drive this trend.

In the past, OEMs would design custom power supplies that could handle the specific voltages and other electrical and physical requirements of their systems. However, time-to-market pressure and the fact that OEMs can no longer afford to make their own power designs has instead steered them toward power system companies to design a solution based on standard power modules.

"The market is driving toward higher currents and toward 'perfect' power, where the power module is expected to convert one voltage to another under all conditions," said Mark Adams, senior vice president of CUI. "More customers are relying on the power module to do the work. They don't have power engineers."

The breakneck pace of technological advances, coupled with the increased emphasis on saving energy, has raised the bar for power systems companies to keep up. "Advancements in semiconductor technologies and system-level performance have had a tremendous effect on the board-level power infrastructure," said Steve Pimpis, Vice President of Strategic Marketing for Murata. "Moore's Law has been driving device densities, with the consequential effects of driving frequencies higher and voltages lower. With as many as 20 different voltage rails on a single board, as low as 0.5V and still falling, and with load currents exceeding 100A, power has become a major challenge for the system architect."

Boom in Digital Power

The boom in power modules was fueled several decades ago by datacom and telecom networks employing a distributed power architecture, which links a front-end AC-to-DC power unit to DC-to-DC modules at each control point. These modules convert the 48V output from the front end to the appropriate voltage. While 5 and 12V were the key voltages in the early days of distributed power, 3.3V and lower voltages have become more common in recent years.

Early on, these systems were analog-controlled. Recent years have witnessed increasing digital control, fueled by sophisticated power management ICs that can perform functions such as sequencing power supplies with controlled ramp rates.

The use of a digital control loop can improve power conversion efficiency, particularly at low loads where excessive energy consumption and waste heat generation can result. A digital control loop encompassing both intermediate bus and point-of-load converters can vary the intermediate bus voltage dynamically to suit varying loads. The input voltage to the point-of-load converter is reduced under low loads, increasing conversion efficiency.

The use of complex ASICs has made it easier to implement tasks such as voltage tracking and sequencing, along with frequency scaling and dynamic core voltage adjustment to control power dissipation. These functions are more conducive to the use of digital power converters.

"We are today confronted with the limitations of analog power technologies that have dominated the power technology landscape for the past four decades," added Murata's Pimpis. "Digitally controlled power modules offer multiple advantages over analog PWM architectures. While such advantages have been understood for some time, practical realization has been delayed by size and cost constraints, but digitally controlled converters have now achieved the cost-benefit threshold that supports their broad adoption."

"The increased demand for energy-efficient power systems and the new technologies developed by the power industry, which are making it possible for systems architects to manage very complex power architectures while saving energy, has contributed to the adoption of digital power and new ways to manage digital power," said Patrick Le Fevre, Marketing Manager for Ericsson Power Modules. "The introduction of digital power has meant that board power modules have moved from being passive units, essentially converting an input voltage to another voltage, to being an integral part of the system including communications with significant interaction between modules and system."

The more active role digital power modules can perform is coveted in not only telecom, but in other industries as well. "Digital power is entering the mainstream," CUI's Adams added. "While telecom has gone to digital for the intelligent functions, medical and industrial will also go for these supplies."

As the use of digital power has grown, the industry has clamored for standards that go beyond the form and fit factor of earlier alliances to include some assurance that the modules are electrically compatible. This will help realize the benefits digital power modules can provide in key functions such as active current sharing, voltage sequencing and tracking, soft start and stop, and synchronization.

Earlier Standardization Attempts

The AMP Consortium has established a roadmap governing the physical specifications, electrical parameters, and interoperability of digital power modules that supersedes several earlier standards efforts.

In 2004, Tyco Electronics Power Systems and SynQor formed the Distributed Power Open Standards Alliance (DOSA), which attempted to establish standards across a broad range of power converter form factors, footprints, feature sets and functionality for both non-isolated (POL) and isolated applications, including intermediate bus converters. This alliance was able to gain the support of fifteen companies, including the three founding members of the AMP Consortium - Murata, CUI, and Ericsson.

While DOSA helped unify the physical specifications for point-of-load modules, it fell short of supplying the needed digital functions required for current and future digital-based power systems, say AMP consortium founding companies.

"The Distributed Power Open Standards Alliance provided for pin compatibility and encouraged innovation, but largely ignored interoperability beyond the scope of the output trim equation," said Murata's Pimpis. "Additionally, the Point of Load Alliance was founded on the principle that member companies would utilize a common chipset to ensure compatibility. While this indeed addressed compatibility, it removed innovation from the equation, and the alliance ultimately failed to maintain pace with advances in power conversion."

In 2004, Artesyn Technologies, Astec Power, and a number of semiconductor suppliers formed a coalition to develop an open communications standard with a power system protocol. This led to the industry standard now known as PMBus.

One issue with PMBus, according to CUI's Adams, is that the command set has been open to different interpretations. "We want to achieve some standardization with how PMBus commands are implemented."

Ericsson's Le Fevre added, "While PMBus commands are standardized, due to the type of controller (i.e. full digital or digital hybrid), not all commands will be supported by the control IC. For instance, one tricky element is that non-volatile memory management as well as RAM and pin-strap configurations can be subject to interpretation. IC manufacturers have made their own interpretations, causing many problems for customers when mixing different products based on different IC suppliers."

Le Fevre added that accuracy and paralleling supplies are also complicated with digital power. "Every PWM IC supplier has its own set of registers and algorithms, making it virtually impossible to parallel a variety of modules if not based on the same controller. Another difficulty is that there is no accuracy requirement on measured parameters (Iout, Vout, Temp, Duty Cycle, etc.) in the PMBus specification. The time stamp of the data is not specified either, which reduces the usefulness of the read data for telemetry operations."

Creating standard command sets and protocols for digital-power modules will also help OEMs during the design-in phase, as many will program the parts for their specific applications at the board level. Standard power modules will reduce stocking requirements for these companies.

"One customer has forty-five rails with digital point-of-load modules," noted Adams. "If they can program these modules on board, there may be only perhaps five different part numbers. But if not, there could be maybe forty-five different part numbers they have to inventory. There is more cost imposed by the manufacturer or distributor to program these modules off the board."

One factor helping the AMP Consortium is that the companies have already agreed to standardize on the digital controller, which is made by Intersil. The Intersil controllers support the microAmp 20 to 25 A and megaAmp 40 to 50 A standards. The controllers provide digital-power features such as automatic compensation, pin-strap current sharing, and Intersil's DDC (digital dc) bus for inter-controller communication. The DDC bus enables system-based sequencing, fault management, and current sharing via a single wire.

Products Emerging

The true barometer of success of the AMP Consortium will undoubtedly be how products are received by OEMs. Thus far, suppliers have kept their promise of introducing a steady stream of products.

For instance, in bus converters, Ericcson offers the BMR456 (quarter-brick) and BM457 (eighth-brick) series. Both parts accept inputs of 36 to 75V or 40 to 60V. The BMR456 produces up to 39A / 468W with 95.2% efficiency, while the BMR457 (Figure 1) produces 25A / 300W with 96.4% efficiency. Other specifications include 2,250Vdc input-to-output isolation, +/-2 percent output-voltage tolerance, and an MTBF of 2.9 million hours.

Figure 1: The BMR456 Quarter-Brick Advanced Bus Converter. (Source: Ericsson)

CUI has developed the NEB-D series of one-eighth brick intermediate bus converters. The converters are designated the NEB-264DW (36 to 75Vdc in, 264W) and the NEB-300DW (40 to 60Vdc in, 300W). The fully regulated converters are designated the NEB-264DW (36 to 75Vdc in, 264 W), and the NEB-300DW (40 to 60Vdc in, 300W). The fully regulated modules are up to 95.2% efficient at half load, 12 V out. They measure 2.3 x 0.89 x 0.4 in3.

In digital point-of-load modules, Murata offers a number of parts compatible with the microAMP™ and megaAMP™ standards. An example is the OKDY-T/40-W12-001-C (Figure 2), a 40-A, non-isolated point-of-load converter with a 4.5 to 14 V input and 0.6 to 3.3 V output. The surface-mountable converter measures 1.215 x 0.787 x 0.323 in.

Figure 2: The OKDx-T/40-W12 series are high-efficiency, digital point-of-load (PoL) DC-DC power converters capable of delivering 40A/132W that comply with the AMP standard designation megaAMP-40. (Source: Murata)

Product availability is expected to increase as the companies introduce additional parts in the Consortium-approved form factors, noted CUI's Adams, "A lot of products are coming down the pipeline."

Outlook

Although there is no guarantee any consortium will succeed, each of the AMP Consortium founders believe their early engagement of industry partners will be beneficial in the long term. "We've been getting a lot of positive feedback from customers," added Adams. "We have been meeting and corresponding on a monthly basis." Cost, of course, is one of the key factors in product selection and system design for OEMs. To date there's no concrete evidence that products meeting AMP Consortium guidelines will be less costly than current solutions; however standard products will likely result in faster time-to-market.

"As with any industry, cost is based on a number of factors and volume is a key driver," Le Fevre added. "Customers are guaranteed to be supplied interoperable products, and as a result we have expectations that volumes will grow significantly and reduce overall costs in the process." Others are likely to benefit from the potential second sourcing products designed to AMP Consortium standards. "In terms of sales channels and distribution, each member has to support direct and indirect sales networks with proper information, training, and documentation. Many activities have already been initiated by all members, which have received a very high level of interest from the field application engineering community," added Le Fevre.