Digital power is on a roll, underscored by Revision 1.0 of the PMBus power management protocol just delivered by the eight founding members of the Power Management Bus Implementers Forum (PMBus-IF). And support for efforts by the group, established only last fall and now under the umbrella of the newly announced System Management Interface Forum—a special interest group (SIG) that includes those involved with the Smart Battery System (SBS) and the System Management Bus (SMBus)—is likely to increase in leaps and bounds.

If nothing else, the new protocol, which is designed to be implemented over the SMBus serial interface, brings a broad, system-oriented definition of "digital power" to the industry. Indeed, its genesis is rooted in IBM- and HP-style systems. "The interface spec represents a lot more than simple power-conversion and feedback loops," said Todd Hendrix, vp of Worldwide Marketing at Artesyn Technologies, one of the eight original companies forming the PMBus-IF. "It could mean that, but actually the spec is much more comprehensive. It's a communications interface for digital power system management that provides a standard language for control and monitoring," he said, noting that products that are suitable for PMBus implementation, or ones that will ultimately be compatible, are already here or in the works. They include the recently announced Fusion line products from Texas Instruments (a founding member of the PMBus-IF coalition), some power management chips from Zilker Labs (another founding member), and the anticipated arrival of several PMBus controllers by mid year.

In that context, the PMBus effort differs from alliances such as DOSA and POLA, which define various form factor, pin-out, and efficiency standards. Nor is the PMBus involved with communications between converters such as for current sharing and voltage tracking. So using the command set for designing individual power converters represents an application that's within the realm of the PMBus protocol, but one that's rather obtuse to its major purpose. In contrast, the PMBus spec defines a common communications link for setting overall operating conditions in any compliant power converter (bricks, point-of-load converters and eventually, AC/DC supplies) as well as system components such as temperature sensors. Typical commands, for example, might be used to set a system's maximum output power or switching frequency, and calibrate various measurement devices.

The protocol itself will be what one expects in the spirit of cooperation—an open standard that's royalty free and whose specifications are available for inspection by anyone. Members of the PMBus-IF will be able to contribute to future specifications and revisions, and participate in working groups for related projects. For more information, visit www.powerSIG.org