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.