New-Tech Europe | September 2016 | Digital Edition

Figure 1. The traditional fixed distributed power architecture is optimized for earlier generations of servers.

It is worth noting, however, that peak power consumption continues to increase to meet demands for increased computing capability. Typical server board consumption has increased from a few hundred watts to 2kW or 3kW today, and could reach 5kW or more in the future. As a result, there is a growing difference between the server’s minimum power at light load and maximum full-load power. Power distribution architectures are becoming more flexible, with real- time adaptive capabilities, to maintain optimal efficiency under all operating conditions. Adapting the Power Architecture Figure 1 shows a typical distributed

power architecture comprising a front- end AC/DC converter that delivers a 48Vdc input to an Intermediate Bus Converter (IBC). The IBC provides a 12V intermediate bus that supplies low-voltage DC-DC point-of-load (POL) converters positioned close to major power-consuming components on the board, such as processors, System on Chips or FPGAs. Multiple POLs may be used to supply core, I/O and any other voltage domains. The 48Vdc front-end output and 12V intermediate bus voltage have been chosen to minimize down-conversion losses and losses proportional to current and distance when supplying typical server boards. However, given the changes in core voltage, current draw, maximum power and difference

between full-load and no-load power, these fixed voltages are less suited to maintaining optimal efficiency. The ability to set different voltages, and change these dynamically in real- time, allows the system to adapt continuously to optimize efficiency. Take Control with PMBus The PMBus protocol provides an industry-standard framework for communicating with connected, digitally-controllable power front- end, intermediate and point-of-load converters (figure 2). A host controller can monitor the status of the converters, and can send commands to optimize input and output voltages and manage other aspects such as enable/disable, voltage margining,

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