Patent Lawsuit Verdict Clouds Future For PMBus

Jan. 17, 2008
The verdict is in on the digital power-control patent lawsuit between Power-One and Artesyn Technologies, and it doesn’t bode well for the PMBus. Maybe Power-One should change its name to “Power- Won” now that a Texas jury

The verdict is in on the digital power-control patent lawsuit between Power-One and Artesyn Technologies, and it doesn’t bode well for the PMBus. Maybe Power-One should change its name to “Power- Won” now that a Texas jury has upheld the validity of its ZOne digital power-management and power-control patents. The jury found the patents to be valid and specifically ruled that Artesyn Technologies infringed on one of the Power- One patents. Artesyn is part of Emerson Electric’s Network Power business unit.

Power-One believes its digital power-management and power-control intellectual property (IP) applies to a range of digital power-control products, systems, communications methods, bus architectures, and implementations. This covers dc-dc point-of-load (POL) implementations using data bus communication, including the PMBus protocols.

Validation of the Power-One patents could put a dent in the future of the PMBus. Power-One CEO Bill Yeates says that if dc-dc POL PMBus users have printed-circuit cards that have multiple POLs and a communication bus, the technology will require a license from Power-One. No license fee has been announced.

It’s not clear if the semiconductor manufacturers that have ICs intended for PMBus applications are subject to licensing their products. It would appear that they would be exempt because they produce components that could only be a part of a PMBus system.

But if their ICs are found in power supplies or customers’ system printed-circuit boards that infringe the Power-One patents, they may stand a chance of being sued. Because of this patent situation, it is likely that the market for their ICs would certainly be reduced, at least in the near term. Several companies already have introduced PMBus ICs.

PMBus on the Market
Zilker Labs’ 3-A, PMBus-compliant ZL2105 combines a synchronous step-down dc-dc converter with integrated synchronous power MOSFETs and key powermanagement functions in a 6- by 6-mm package.

The IC is fully configurable with simple pin-strap connections or resistor selection or via the device’s on-board serial port using the industry-standard PMBus command set. It also provides the configurability, control, and monitoring capabilities of digital power technology without compromising efficiency.

Intersil’s ISL8601 is a single-phase pulsewidth modulation (PWM) controller with integrated MOSFET drivers utilizing analog voltage mode control. Its extensive PMBus compliance enables flexible power-supply design and comprehensive product evaluation and testing. Besides the I2C interface, select PMBus commands for the ISL8601 can also be programmed via external resistors, bringing the power and flexibility of PMBus into low-cost power-supply systems.

The LTC7510 from Linear Technology is a digital dc-dc controller with onboard nonvolatile memory and a PMBus interface for real-time reporting and controlling of POL power-management attributes such as current, voltage, and operating frequency and temperature. Power-supply sequencing, margining, and turn-on/off are easily programmed via the PMBus interface. The LTC7510 also provides extensive POL fault-detection reporting capability.

Maxim’s MAX8688 integrated digital power-supply controller and monitor IC can work with any existing POL power supply to provide complete digital programmability. It operates using a PMBus-compliant communication protocol and can be programmed using this protocol or simply with the use of a free GUI available from the Maxim Web site that significantly reduces development time. Once the configuration is complete, the results can be saved into EEPROM or loaded onto the part through PMBus at power-up.

Primarion’s PX75xx family incorporates an industry-standard PMBus serial interface for controlling and monitoring. Digital PMBus-compliant POL power ICs are designed for use in synchronous buck converters. Applications include low-voltage distributed power supplies required to power ASICs, FPGAs, DSPs, and memory for telecom, datacom, server, and storage equipment.

The PX75xx family includes the PX7510 single-phase digital integrated power conversion and management IC; the PX7520 dual-phase digital integrated power conversion and management IC; the PX7522 digital dualoutput/ dual-phase integrated power management and conversion IC; and the PX7542 dual-output, multiphase digital dc-dc controller.

The UCD9112 from Texas Instruments is a dual-phase synchronous buck digital PWM (DPWM) controller designed for POL power applications. It integrates dedicated circuitry for dcdc loop management with a microcontroller core, flash memory, and PMBus interface to support configurability, monitoring, and POL management.

The UCD9112 can operate at switching frequencies of up to 1 MHz. The UCD7230 synchronous buck driver works with the UCD9112. Besides its 4-A output drive capability, the driver integrates current-limit, short-circuit protection as well as undervoltage lockout protection. The UCD7230’s 3.3-V, 10-mA linear regulator provides the supply current for the controller.

The infringing power supply referred to in the lawsuit was Artesyn’s DPL20C, which is now said to be “in development” and “coming soon” on the Artesyn Web site. The DPL20C was the first PMBus-compliant dc-dc converter to be announced in September 2005.

Rated as a 20-A output, non-isolated POL dc-dc converter, it featured an extensive set of digital configuration, monitoring, and diagnostic facilities accessible via the PMBus interface. It also boasted a 4.5- to 13.8-V input, 0.6- to 5.5-V programmable output, 20-A output with 91% typical efficiency (12-V input), and differential remote sense. Protection features included overcurrent and overvoltage.

Z-One vs. PMBus
Digital power management provided by Z-One and PMBus lets designers set a power supply’s operating parameters, monitor its operation, and perform corrective measures in response to faults or warnings. The ability to set a power supply’s output voltage allows the same hardware to provide different output voltages by merely reprogramming. Plus, the ability to monitor and maintain a power-management subsystem enhances its reliability and availability.

The Z-One digital system and PMBus differ in how they partition powermanagement tasks (see the figure). Z-One products split the power-management responsibilities between a firmwareenabled digital power manager and a POL-based DPWM IC. The PMBus requires the designer to program the computer according to the PMBus protocol with much of the intelligence residing in a system controller.

Also, the Z-One system operates only with dc-dc converters, whereas the PMBus can operate with dc-dc and ac-dc converters. It should be noted that the PMBus is just a protocol, not the actual hardware.

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