EEbeat

By Mark Adams
For years now we have all read that digital power is the wave of the future for system power design, with report after report forecasting impressive compounded growth rates in this space. This is not another diatribe on digital power taking over the world.  Instead, my intention is to highlight a very real barrier that exists to engineers who want to design a fully digital power system. The power industry has failed to recognize the importance of interoperability to the end customer.

Interoperable is defined by IEEE as the ability to exchange and make use of exchanged information between 2 or more components or systems. In 2004, this was a key area of focus for the founding members of the PMBus (Power Management Bus) group, the standard by which the majority of the digital power companies and OEMs adopt. This seems great in theory— an open standard, clearly defined, and widely supported by all.  Unfortunately, it isn’t as straightforward as that. PMBus does not ensure interoperability. PMBus does a great job of defining the structure for a majority of the functions from a system level, but does not define other critical features.

The semiconductor companies that are designing digital PWM controllers for this space have excelled at driving innovation and differentiation. This differentiation, however, has driven a divide in the communication barrier. The issue is the development of a second serial bus, in addition to the SMBus, to handle high speed communication between the devices. This second serial bus is proprietary in both the physical implementation, as well as the usage. As a result, the ability to have a truly interoperable system at the POL level has been eliminated, unless you only use one controller company across the board.

In order to achieve a true interoperable digital system that includes fault management, current sharing, and other power management functions, designers need to pick a company/controller family of choice. The existence of the proprietary serial bus will prevent designers from using more than one company’s controller.   At first glance, this doesn’t appear to be a big deal for companies. A designer will more than likely select a controller company of choice and utilize that controller company for their discrete designs, similar to their usage of MCUs or FPGAs.  The issue arises when designers want to have a mix of higher power POL modules and down/discrete designs, or design 100% of their power rails utilizing modules. These companies will need to align their designs to ensure that the selected module company uses the same controller as the discrete portion of the design, or, in the case of a power system exclusively utilizing 100% module power system, that the power module companies use the same controller.

The CUI team didn’t discover this until early 2011 after it was announced that we had entered into a cooperation with Ericsson regarding the second sourcing of POL products.  Through a thorough examination into the required PMBus commands, the physical layer that supported each of the commands, and the physical and command structures of the additional module features, we found that CUI would have to adopt a second controller into our digital power portfolio in order to offer a true second source option to the Ericsson modules.I believe that the majority of vendors in the digital power space don’t understand that this creates a problem for customers. The assumption among semiconductor and power supply companies has always been that PMBus would allow their ICs or modules to talk to the competition within a power system.

In order to address this issue in the digital power arena, CUI is moving forward with a mixed controller solution platform. While other power supply companies typically offer a portfolio based on only one controller, CUI has developed a roadmap that will provide customers with the ability to pick a controller family that best fits their needs.  Today CUI offers 2 different controllers in our Novum® Advanced Power POL product family, Intersil/Zilker Labs and Powervation. Going forward it is our intent to become a controller-agnostic company. As a power supply manufacturer, it is our job to provide our customers with the best digital controller technology available in our modules, allowing them to make the decision that fits their specific needs.

Systems are growing more complex with each successive product cycle, as are the power requirements.  Digital power provides a number of benefits that have the potential to optimize these complex systems, but we are finding that communication has become a critical barrier to taking full advantage of this technology.  At CUI, our approach is to create a platform that breaks down this barrier and offers designers true interoperability within their digital power system.   

Mark Adams will be speaking further on this topic at APEC 2012 on February 7^th. For details please visit http://www.cui.com/News/Press-Releases/CUI-to-Present-and-Exhibit-at-APEC-2012.