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48V-to-1V Conversion – the Rebirth of Direct-to-Chip Power

48V-to-1V Conversion – the Rebirth of Direct-to-Chip Power

Jul 28, 2017

This post was originally published May 26, 2017 on the web site . Learn more about eGaN technology and EPC GaN solutions for 48 V to Point-of-Load.

During last week’s PCIM Europe event in Nuremberg, Germany, direct 48V-to-1V power conversion architectures were a significant topic, mostly outside of the exhibit floor. Vicor was quietly showing its latest generation of 48V direct-to-chip power components. Ericsson Power Modules and Efficient Power Conversion were holding invitation-only meetings where future designs of 48V direct to load power conversion architectures were the focus of the discussions. By the end of 2017, several vendors are expected to be offering dc-dc converters delivering 48V-to-1V direct conversion.

Direct-to-chip power is not a new concept. During the 1980s, 48V-to-5V conversion was the preferred architecture used to power ICs in telecommunications installations. But when IC operating voltages began dropping below 5V, direct-to-chip power become unfeasible. As a result, a variety of intermediate bus architectures (IBAs) employing multi-step voltage conversion were developed to power telecommunications equipment and datacenter racks.

Today, new topologies and new technologies such as digital control loops and GaN power devices are again enabling the design of direct-to-chip power architectures, even with IC voltages as low as 1V. These modules, which allow contemporary low-voltage, high-current CPUs, GPUs, ASICs and DDR memory to be powered off of a 48V distribution bus, enable unprecedented power density, conversion efficiency and low power system distribution loss.

Evidencing advances in power conversion engines, control systems and modular power technology, Vicor's latest 48V modules were introduced following the Open Compute Project ("OCP") Summit 2016 at which Google announced its initiative to promote 48V server and distribution infrastructure as a standard for data centers. At that time, Patrizio Vinciarelli, President and CEO of Vicor, commented: "By developing its 48V server infrastructure, Google pioneered green data centers. And by promoting an open 48V rack standard, Google is now enabling a reduction in the global cloud electricity footprint."

"Racks in data centers are consuming more power, today's 15kW rack will soon consume 40kW," observed Martin Hagerdal, President of Ericsson Power Modules. "The use of direct conversion will become necessary at those high power levels. And it will bring numerous benefits such as more efficient power conversion, lower-loss power distribution, easier thermal management, enhanced transient response, the use of less board space by power converters and both lower initial system cost as well as lower operating costs," Hagerdal stated.

"Ericsson will be introducing our first-generation direct conversion 48V-to-1V board mounted dc-dc converters in the fourth quarter of this year. Those designs will be enabled by advanced digital power technologies," said Hagerdal. "Further in the future, possibly sometime in 2018, we will introduce direct conversion dc-dc converters using wide band gap semiconductors such as GaN."

"Vicor has pioneered 48V direct-to-chip power conversion. Our latest generation products expand a family of VTM and PRM modules that have exhibited substantial improvements in each generation. Over the past decade, Vicor has, in fact, reduced converter power loss by an average of 25% every two years while increasing power density. Compared to solutions using traditional "multi-phase" buck regulators, Factorized Power offers superior efficiency, density, transient response and noise performance. A third party study has recently demonstrated that the VTM's noise spectrum is an order of magnitude lower than legacy multi-phase buck regulators," stated Vinciarelli.

Like Ericsson, Vicor is investigating the use of wide band gap semiconductors for next-generation direct-to-chip dc-dc converters to enable even higher levels of performance.

"The use of GaN switches in 48V-to-1V direct dc-dc converters can improve system performance by 30%, compared with today's best silicon-based designs," commented Alex Lidow, President of Efficient Power Conversion.

"And GaN will give power designers a variety of performance choices between efficiency, density, cost, and transient response," Lidow stated "At EPC, we have analyzed the performance tradeoffs of several design approaches using GaN including: a traditional two-stage isolated IBA; a single-stage buck converter; a two-stage non-isolated IBA; and the transformer-based half-bridge with current doubler as proposed by Texas Instruments.

"The two-stage non-isolated converter provides both the best power density and the lowest cost," Lidow observed. "But the significantly less dense transformer-based half-bridge with current doubler architecture provides the highest overall efficiency, but with lower performance in terms of transient response and a substantial cost penalty," continued Lidow.

EPCs 48 volt to 1 volt road map

"EPC has an eGaN integrated circuit road map that will lead to even higher levels of performance," Lidow commented. "We will be developing a monolithic half bridge, an integrated FET and low side driver, an integrated half bridge with level shift and drivers, and ultimately a monolithic buck IC," Lidow concluded.

Efficient, dense, cost-effective and reliable power distribution is a critical element in data centers and other distributed electronics applications, such as autonomous driving vehicles and LED lighting. Although the benefits of a higher distribution bus voltage, particularly 48V, which requires no special safety precautions, are well known (smaller cables and bus bars, lower distribution losses, smaller storage capacitors), conventional power conversion approaches have not been able to efficiently, or compactly, transform power from a 48V bus into the low voltages (e.g., 3.3V, 1.8V and 0.8V) and high currents required by contemporary CPUs or GPUs.

As a result, CPU power conversion has customarily relied on 12V distribution. A 12V bus, however, must carry four times the current carried by a 48V bus, and, because distribution losses are a function of the square of the current, the power lost in a 12V bus can be as much as 16 times the loss in a 48V bus. By providing efficiencies from a 48V bus that are better than 12V legacy solutions, in a fraction of the space, 48V direct-to-chip power conversion will enable system designers to implement green distributed system solutions featuring high conversion efficiency, high power density and low distribution loss.

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