How Vicor is Transforming Datacenters from 12V to 48V

Announcements by Google at the OpenPOWER Summit and the Open Compute Project (OCP) U.S. Summit are recent industry proof points of a shift to 48V server and infrastructure. The shift from conventional 12V server racks to 48V racks is expected to reduce energy losses by over 30% but there are additional challenges within servers and datacenters that drive a change from 12V.

Conventional Power Design

Higher current and lower voltage CPU requirements triggered the use of multi-phase power schemes for CPUs. This power scheme was derived to manage the “energy vs. size” power inductor shortfalls. From their debut, multi-phase designs have faithfully powered CPUs for at least two decades now. Through time, enhancements have been made to this power scheme following the industry trends in MOSFET and magnetic improvements. More recently, advanced power management schemes have been implemented dynamically engaging only the number of power phase stages needed for power, otherwise called dynamic phase shedding.

More, More, More…

But, all these improvements do not eliminate the basic flaw of energy storage/delivery vs size of the magnetics. Therefore, as CPU power demands have increased, the number of power stage phases required to power a CPU have increased. Peak currents have further exacerbated the number of power stages required by increasing peak power.

The ever growing demands of CPU power is only one issue for newer server designs. While server CPU power demand is growing, the allowable space for power on the board is decreasing. Higher density and higher power also heightens signal integrity issues or how power converter pollutes neighboring data lines of the CPU.

Why 48V?

Distributing power in a server rack and on the server board creates losses. These losses are calculated by the resistive losses including copper buss bars, wires, and PCB traces. Transmitting power at 48V vs 12V provides a 16x power loss reduction for the same amount of power transmitted. A 16x saving is hard to achieve any other way. But, historically, the desired gain in transmitting at 48V came with performance limitations converting the 48V to the CPU voltage. One limitation is efficiency when compared to conventional 12V multi-phase designs. That is, the efficiency gains made in distributing at 48V have been historically given back when converting from 48V (less efficient than 12V conversion). Size also matters with historical 48V power conversion designs consuming much more of the board area than a 12V design.

How Vicor did it -> 48V Direct to CPU

Vicor approached CPU power with its proven architecture called Factorized Power. This architecture abandons the conventional multi-phase power scheme along with all of its limitations. The Vicor approach enables 48V direct to CPU power conversion with a limited set of components.


Figure 1

The inset picture in figure 1 highlights the equivalent 12V multi-phase solution required in addition to a 48V to 12V converter.

Efficiency – Match 48V conversion to 12V

The Vicor Factorized Power architecture may look like two stages of conversion but it is actually one stage divided between two components delivering 48V direct to CPU. The first stage (the PRM) handles pre-regulation only, utilizing a high performance Zero Voltage Switching (ZVS) topology. The second component (the VTM), handles the voltage transformation of the regulated voltage to the CPU voltage using a Sine Amplitude Converter (SAC) topology. By dividing the conversion into its regulation and transformation functions (and implement innovative switching technologies within each), conversion from 48V can achieve efficiencies of the conventional 12v multi-phase.

Size – Enable a Single Component Power near CPU

Real estate on a high density server board is precious and even more so around the CPU itself where hundreds if not thousands of I/O is routed to and from the CPU.

Figure 2

Figure 2

But power for the CPU needs to be placed near the CPU. The Vicor solution requires only a single component to be placed within the precious CPU area (Buck Boost pre-regulator can be placed at the edge of the PCB without penalty). This creates a 50% or more space reduction over conventional 12V multi-phase designs.  See Figure 2.


What’s next?

The Vicor 48V Direct to CPU solution is enabling servers to leverage the benefits of 48V by overcoming the historical limitation in 48V conversion. In addition to breaking the 48V barrier, the Vicor solution also provides performance over conventional designs creating a continuing path forward for next generation, higher power CPUs.


Figure 3

The high density VTM enables not only easy placement near the CPU but can also be utilized within the CPU. Placing the VTM functionality within the CPU package eliminates the short but critical distance delivering the low voltage/high current between the power converter and the CPU (further eliminating losses). Additional benefits include simplifying the layout /density concerns around the CPU and eliminating the majority of power pins required by the CPU package enabling more CPU I/O flexibility and capacity.



References / Additional Reading

Google and Facebook share proposed new Open Rack Standard with 48-volt power architecture, Google Cloud Platform Blog, August 4, 2016

Efficiency: How we do it, Google Data Centers

Google, Intel Prep 48V Servers, EETimes, January 21, 2016

48V: the new standard for high-density, power-efficient data centers, Electronic Products, July 11, 2016

48V Direct to CPU – Solving the Challenges in CPU Power Delivery, Vicor Corporate Website

 Introducing Zaius, Google and Rackspace’s open server running IBM POWER9, Google Cloud Platform Blog, Friday, October 14, 2016


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