[Technology Report]
It's Z-One Vs. PMBus In Digital Power Management
A court decision could determine the future of the competing architectures as well as that of digital power-supply management.
Sure, designers of embedded computer systems know digital techniques. But they may not be intimately familiar with the digital management of the power supplies used by their systems. Two methods reign when it comes to implementing digital power management. Yet it's not clear which method will win the favor of system designers—or the favor of the courts.
Power-One's proprietary Z-One system was the first method to arrive. Then came the open-standard Power Management Bus, or PMBus. More than 30 companies have adopted PMBus, including power-supply companies and IC manufacturers. Meanwhile, Power-One has sued Artesyn Technologies, now part of Emerson Network Power, claiming that the company infringed on its valid digital power-management patents.
As part of a Markman hearing, a U.S. district court ruled in March 2007 in favor of Power-One for most of the important issues related to digital power management. (A Markman hearing refers to the Supreme Court ruling on Markman v. Westview Instruments Inc., which states that a trial judge will decide on the asserted patent claims.) Next, a jury will deliver its decision. Power-One's jury trial is set for this month, and the outcome could determine the future of power-supply digital management.
A recent Supreme Court decision casts a cloud over this patent litigation. The Court adopted a new standard that makes it easier for patents to be denied or challenged on the grounds of being too obvious for patent protection (see "Patent Law: Who Knows What's Obvious?"). The patent ruling could also subject existing patent holders to litigation over obviousness. Some experts say the ruling protects the country's competitiveness, whereas others wonder whether the ruling will hurt innovative firms, such as startups and small companies.
A jury decision in favor of Power-One could prevent anyone from using the company's patents that describe the digital management of power supplies. Ideally, Power-One would like to license the technology, which would expand its applications. If the jury rules against Power-One, then it would appear that the PMBus can be used by anyone that meets its documented specifications (see "The Patents In Question" at www.electronicdesign.com, Drill Deeper 16122).
Digital power management is set up on a basic principle: Power-supply hardware would include links that allow the setting of a converter's output voltage and other operating parameters and then monitor operation to ensure it's functioning properly. Thus, similar power-converter hardware could be used throughout a system.
Initially, a graphical user interface (GUI) would set the operating parameters of all power converters, and the digital power-management system would function as programmed. Then, the digital power-management system would monitor all power converters and notify the host of any failures or performance degradation.
THE Z-ONE SYSTEM Power-One's Z-One architecture integrates a power system's management and power conversion functions. According to the company, this cuts overall system-level costs by 20% to 50% compared with more conventional approaches.
In addition, it allows up to 32 point-of-load (POL) converters to fully communicate with each other under the control of a digital power manager (DPM). Each of these digital Z-Point-of-Load (Z-POL) converters operates with a 3- to 14-V input (except for the ZY8160, which is 8 to 14 V) and provides a programmable 0.5- to 5.5-V dc output.
The Z-One system employs a single-wire Z-One Digital Bus controlled by the DPM (Fig. 1). This high-speed bi-directional bus, which provides both frequency synchronization and data transfer, can access all Z-POL converters in a single communication cycle. The bus carries all of the information to and from the Z-POL converters and DPM, including all operating parameters for each POL converter.
Operational parameters, such as the output voltage, sequencing, tracking, monitoring, interleaving, and protection thresholds, are user-programmed via the GUI and stored in the DPM. At system startup, this stored information programs the Z-POL converters.
After system programming, ongoing communications between the DPM, Z-POLs, and host system support intelligent operation. Designers can repeat this point-and-click process for power-system optimization. The GUI need only be interfaced with the power system during programming, and it can be easily reconnected to support power-system design changes.
Communications with the host system use the industry-standard I2C bus communication protocol. Besides remote programming of each POL, the latest status information of each POL (output voltage, output current, and temperature) is stored in the DPM and can be transmitted to the system.
Hardware for the Z-One system integrates two ASICs, the ZM7300 DPM, and the maXyz ZY7000 series of Z-POL converters. The ZM7300 DPM programs and controls sequencing, tracking, supply supervision, and intelligence with the aid of analog-to-digital converters (ADCs). C&D Technologies is a second source for the Z-One system components.
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