Power Electronics

Initiative Seeks Standard for Digital Power Management

Artesyn Technologies and Astec Power, a business of Emerson, have formed a coalition of power supply and semiconductor manufacturers to develop and support a new communications standard defining an open architecture for power systems control. The digital protocol, referred to as “Power Management Bus” or PMBus, will be implemented over the industry-standard I2C serial bus.

The founding group is composed of companies from both the power supply and semiconductor industries. In addition to the power supply manufacturers Artesyn and Astec, semiconductor participants include Intersil Corp., Microchip Technology Inc., Texas Instruments, Volterra Semiconductor, Summit Microelectronics and Zilker Labs Inc.

Bharat Shah, VP marketing-DC-DC Products for Emerson Network Power’s Astec Power division, said, “Having a truly open standard communication protocol is a must for industry-wide acceptance of digital architectures, and Astec Power is delighted to be a part of this working group.”

The proliferation of different supply voltages across the pc board, in combination with varying device requirements for supply sequencing, tracking, margining and monitoring, is making board- and system-level power management increasingly complex. As a result, many of the on-board dc-dc converters are being redesigned to incorporate programming, control and real-time monitoring functions that were not previously included in the converters. This trend is shaping the development of both isolated and nonisolated converters. The PMbus digital protocol is intended to establish an open, industry-standard communication format to support future power converter products.

While there are existing products and emerging solutions for power system management, the PMbus digital protocol addresses the desire of OEM customers to have open standards that result in multi-sourced products. An open standard could allow OEM customers to continue to design their power systems using discrete components (i.e., embedded converter designs built around PWM controller ICs) or turnkey converter solutions (i.e., off-the-shelf, dc-dc converter modules). Once the new protocol is adopted, the OEM will be able to control all compliant dc-dc converters using the same set of commands, without the need for proprietary silicon or software interfaces.

Though the protocol will establish a common command set for configuring, controlling and monitoring dc-dc converters, it will not dictate how those commands are generated. For example, if the intent was simply to perform margining of the point-of-load voltages in production, the necessary control signals could be generated by existing automated test equipment. On the converter end, there will need to be some form of digital control within the converter. That control might be implemented as an analog PWM controller with some type of microcontroller performing supervisory functions or perhaps as a fully digital PWM controller. In addition, it’s likely that each converter will require some nonvolatile memory on board to store setup and other information.

The PMbus digital protocol will encourage continued product innovation by removing a primary barrier—the lack of a communications standard among power converters and power ICs from different vendors. The protocol will be scalable, initially allowing for the control of more than 100 converters. The first revision of the PMbus digital protocol specification is now in the final stages of completion. The details will be released within the next 45 days and will be circulated to the industry for review and further comments.

Products implementing the new protocol will not be far behind. According to Todd Hendrix, VP of Worldwide Marketing at Artesyn, his company expects to demo converter products using the PMBus protocol by the end of this year, with sampling of such products to follow in Q1 of next year. These products are expected to reach production in Q2.

An overview of the new power management protocol was recently presented at the Darnell Group’s Digital Power Forum 2004 held in San Jose, California in the paper “Considerations For A Power System Management Protocol,” by Robert V. White, staff engineer in the Artesyn R&D group.

This paper is available in the Digital Power Forum proceedings, which may be ordered on the web at digitalpower.darnell.com/digitalpower/.

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