From Scepticism to Necessity, Digital Power Adoption Accelerates for Next-gen Data Centers
Everything’s going digital, so why not power supplies? If you had asked data center/server design teams about their views on digital power as recently as a decade ago, the responses would have ranged from "doesn’t make sense, power is inherently analog" to "maybe, but…" or even "sounds like a good idea, but not yet," due to concerns about implementation, integrity, and cost.
Digital regulation of power-supply rails for DC-DC converters is now the preferred technique in demanding applications due its efficiency, size, performance, and flexibility
Everything’s going digital, so why not power supplies? If you had asked data center/server design teams about their views on digital power as recently as a decade ago, the responses would have ranged from "doesn’t make sense, power is inherently analog" to "maybe, but…" or even "sounds like a good idea, but not yet," due to concerns about implementation, integrity, and cost.
Jump forward to the present and the answers are quite different: "It’s no longer an option, it’s become essential, " and "we couldn’t do what we need to do without it." The benefits in performance, efficiency, cost, footprint, and flexibility for these supplies, which are so critical to effective sever/data center performance, are dramatic, demonstrated, and undeniable.
So, what is digital power? It’s the use of digital circuitry in the inner control loop of a DC-DC regulator, instead of the traditional analog closed-loop control, or the half-way step of analog control but with high-level digital supervision. In digital power, critical supply currents and voltages are digitized and then processed by internal firmware-based algorithms, which manages the regulator to maintain a constant voltage output despite changes in load or other factors.
Digital power has already passed the critical inflection point in adoption. According to market-research firm IHS, "the worldwide market for DC-DC converters with digital control is forecast to nearly double from $600 million in 2014 to over $1.1 billion by 2017."
Why this increase in digital power uptake? The answer is simple: it’s the only feasible way to meet the increased power demands and address the associated management issues of typical data center/server board, with its many separate DC rails per board (between 12 and 20 unique rails is not unusual). Further, only digital power can support the exponential growth in load demands, as per-board power requirements in the data-server segment have increased by a factor of four (from just 300W to 1200W) since the early 1980s. Estimates are that it has already reached 3kW per board in 2015, and some studies are forecasting power consumption of 5kW/board by 2020.
The top-tier benefits of digital power are clear: higher efficiency, which means reduced operating cost and thermal dissipation (and resultant heat which has to be removed); smaller footprint (which frees up valuable PCB real estate); and ability to meeting increasingly stringent regulatory mandates.
Digital power’s virtues go beyond these obvious ones, driving its further acceptance at power levels even below the 25A-to-100A range where it has already had its greatest impact. Among the benefits are:
- Greatly enhanced management and oversight, where the supply can report performance and operational data to the server controller, and also dynamically change key operating points and parameters as directed, in order to meet changing circumstances.
- Smart sequencing, where each of the numerous power rails can be ramped up and down in any order, with ramp up/down timing as needed; this sequencing can even be changed on-the-fly.
- Adaptive control algorithms provide better performance than the single hardware-based control tactic of the analog power supply.
- The flatter curve of efficiency versus load means a digital supply can provide superior performance even when lightly loaded, which saves additional power.
- In addition to the smaller footprint – a valuable attribute, but one for which it is hard to provide a quantitative price – it simplifies the BOM with fewer passives; and requires lower-value bulk capacitors for output filtering, resulting in reduced component height and so enabling closer spacing between boards.
As impediments are overcome, barriers to adoption shrink
As with any relatively new and dramatically different architecture, there have been concerns (many of them legitimate), especially given the cautious, conservative world of power supplies. These included hesitation due to unproven reliability and performance in the field; potential difficulties with user set-up and configuration due to the inherent flexibility in parameter and functionality selections; and issues related to lack of multiple sources for a chosen supply.
Each of these concerns has been addressed in the past few years, further removing any residual impediments to increased adoption of digital power, while extending its viability to lower and higher power levels:
- For reliability, the huge number of high-intensity, high-reliability installations in the field, with millions of cumulative operating hours and logged data, has provided solid numbers on the actual performance along with the benefits and savings.
- For configuration, tools such as the Ericsson Digital Power Designer (EPD) Graphical User Interface not only simplify the set-up task, but make it easy for engineers to evaluate the trade-offs and judge "what if" as they adjust parameters to meet multiple, sometimes conflicting objectives.
- For sourcing, the Architects of Modern Power (AMP) consortium, established in 2014, provides users with compatible power products with common control and communication commands and configuration files. The founding members of this power industry consortium are Ericsson, CUI Inc., and Murata, each with considerable experience and a solid track record in digital power. As other vendors join, issues related to second-sourcing, or pricing fears due to a sole source’s position, will be further reduced.
As the recently departed baseball legend and philosopher Yogi Berra pointed out, in a truism that industry observers should always keep in mind: "It’s tough to make predictions, especially about the future." Still, the trend lines are very clear: growing demand for increased power capacity per board in servers and data centers, along with pressures for lower operating costs and better performance, can only be met by digital power approach.
Digital power offers much more than just improvements in basic, critical factors such as efficiency, footprint, and cost improvements. The additional features and functions it inherently delivers are the only way to implement the new strategies for system-level management and control that are needed for tomorrow’s complex, multi-rail, higher-power boards.
According to researchers at IHS, the market for digital power supplies and their constituent components will grow between 3.5x and 5x between 2014 and 2018
