News and New Products

Power-industry coalition announces PMBus standard, forms SIG

Margery Conner, Technical Editor -- EDN, 4/28/2005

A coalition of power-supply and semiconductor companies led by Artesyn Technologies has released version 1.0 of the PMBus (Power Management Bus) specification, which defines a protocol to manage power converters and a power system via communication over the SMBus digital communication bus. The coalition has also announced the formation of a special interest group (SIG), the System Management Interface Forum (SM-IF), to further develop and promote the PMBus power operating system. The SM-IF comprises two technology groups: The PMBus Implementers Forum and the Smart Battery System Implementers Forum. SM-IF will also take over responsibility for the SMBus.

The SMBus is essentially compatible with the I²C bus, a popular 2-wire bus that handles inter-IC control. "The I²C bus is a highly prevalent interface on embedded microprocessors—it's just all over the place," said Michael Stefani, director of product marketing for Artesyn. "SMBus adds an alert line to I²C, making it just a short step from I²C to SMBus."

In addition to Artesyn and Astec Power, the initial coalition comprises semiconductor manufacturers Intersil, Microchip Technology, Texas Instruments, Volterra Semiconductor, Summit Microelectronics, and Zilker Labs.

Conspicuously absent from the SIG is Power-One, which launched its proprietary Z-One bus last year and announced a design, manufacturing, and marketing agreement with C&D Technologies in December. "For complex systems, Power-One has found that the PMBus does not provide a configuration-controlled, standardized programming interface like the Z-One GUI," said Dave Hage, executive vice president of Power-One. "Lack of standardization in PMBus converters could make the creation and management of a uniform PMBus GUI virtually impossible."

Moreover, a bus architecture is overkill and adds too much expense to some low-end designs, Hage said. "For low-complexity systems, customers have requested a configurable POL (point of load) that does not require a bus and is more cost effective." For these applications Power-One developed its "No Bus" Z1000 POLs.

The PMBus 1.0 specification is available here, and more information on the SM-IF is available here.

Artesyn Technologies, www.artesyn.com

System Management Interface Forum, www.powersig.com

Power Management Bus Implementers Forum, http://pmbus.info/specs.html