2019 OCP Global Summit

The renewed interest in Direct Conversion, using isolated DC-DC converters to convert power from a 48V bus in data centers directly down to voltages suitable for powering processors, FPGAs and ASICs, can be attributed largely to energy savings. In December 2017, it was reported that data centers consume about 416 terawatts globally (Forbes) and, with the explosion in cloud computing, the figure is surely higher now and set to increase dramatically. Small percentage savings are therefore valuable in terms of cost reduction and reduced environmental impact. Today’s power distribution architectures typically convert either AC or 48V DC to an isolated 12V, which is routed around server racks with non-isolated point-of-load converters providing the final step-down in voltage. As the rack loading has ramped up, however, the current at 12V has become increasingly unmanageable, causing significant ohmic distribution losses. Dual conversion of 48V to 12V, then 12V to load voltage, has also been a source of losses, even with end-to-end efficiencies of about 89%. A solution already adopted by Google and Facebook in their standard Open Rack v2.0 is to eliminate the 12V bus for the very highest current demands and convert 48V directly to the load voltage – the Direct Conversion approach. In this arrangement, 48V is distributed directly to the server blades, and an isolated converter on the board close to the load provides precise regulation where it is needed. This approach had been adopted in the past, when end voltages were typically 5V or 3.3V, but the conversion technology of the day was too inefficient at voltages lower than these. Technology has now advanced, to the point where an isolated 48V to 1V converter can be more than 92% efficient: a 2% to 3% gain over the IBA approach. Benefits are wide-ranging: current at 48V is a quarter of the 12V value for the same power, yielding a sixteenth of the losses in comparable cabling and bus connections; overall footprint is smaller, with a single conversion stage, and hardware costs lower; cooling requirements are reduced, and energy saved with a more efficient process. The modern design of the new Direct Conversion DC-DCs also facilitates extra functionality such as Adaptive Voltage Scaling (AVS) for optimal processor speed and energy draw, and a serial voltage ID interface. Full digital control of the converters is typical, with programmability through an I2C PMBus interface. The first products from Flex Power Modules, based around ST microcontrollers, provide a modular multi-phase solution. There is a 70A “main” unit with a footprint of 28mm x 12mm, while up to five additional 70A “satellites” in the same footprint can be added as needed, up to 420A in total. This approach offers efficiency optimization across a wide range of current demands, with the addition of automatic phase addition and removal where demanded by the load. With a 1.0V output, a nearly flat efficiency of 92% is provided across most of the load curve. Even with all the advantages Direct Conversion affords, the marketplace insists on having a broad base of suppliers. To that end, Flex Power Modules is expanding the 48V ecosystem for Direct Conversion. Now that Flex Power Modules has introduced products, and continues with a product roadmap, the ecosystem is here and growing. Flex is one of the founders of an industry alliance, the Power Stamp Alliance (PSA), further promoting the expansion of the 48V ecosystem. The PSA is a collaboration between founding members Flex Power Modules, Artesyn Embedded Technologies, Bel Power Solutions and STMicroelectronics to offer Direct Conversion products. It sets functional and mechanical standards for these new Direct Conversion products, with each member free to set the topology utilized and detail design. This presentation will highlight the key technical features and benefits of the 48V Direct Conversion approach in OCP platforms, as well as highlighting the commercial benefits of an open alliance such as the PSA.