From e-mail to online buying and selling, social networking to gaming, and VoiP telephony to video on demand, recent years have seen exponential growth in e-commerce, internet communication, and online or downloadable entertainment. This growth has fuelled ever-increasing demand for the electronic systems – many of them in secure data centers - that are needed to store, process and transfer the underlying electronic data 24 hours a day, 365 days a year. And there are very real economic, legislative and environmental pressures to make these systems as efficient as possible.
A ‘typical’ data center will include servers, storage area networks, routers and switches. In the past, these centers have often been measured on their performance density (MIPS/m2). However, this is changing for a number of reasons.
Firstly, lifetime operation costs for the equipment in the data center are now estimated at about three times initial capital outlay. Secondly, an increased concern on the environmental impact of electricity usage is driving legislation to maximize efficiency. And, thirdly, there is genuine concern that, without efficiency improvements, many data centers are going to be unable to handle the growth in processing power and supporting infrastructure needed to meet demand.
As a result, the key Figure of Merit (FOM) metric as we move forwards is performance efficiency, or MIPS/W. And, by improving both equipment efficiency and the efficiency of the supporting infrastructure, the latest power semiconductor technologies are playing a significant role in driving up this Figure of Merit.
Power consumption in the data center
We can identify two general sources of power consumption in the data center. The first is the processing, storage, switching and routing equipment itself. The second is the infrastructure required to cool and protect these servers, storage networks, switchers and routers. The energy usage from each is about equal and they are directly related.
Equipment energy consumption consists of three main elements. The electronic loads such as microprocessors and memory banks consume 60 to 70 percent of energy, while power supplies consume 25 to 30 percent, and cooling uses five percent.
While there have been significant advances in reducing the load’s power profile (for example, the introduction of multi-core efficient processors and virtualization technology), there are other opportunities for engineers to significantly reduce the consumption of all three of these major energy consumers. New ‘smart power’ management systems, for example, include the co-design of several critical components of the power supplies that are integrated into the platform. Based on advanced power semiconductor technologies, the key elements of these power systems are highly-efficient and dense power stages, advanced highly responsive power controllers, digital interfaces for programmability and diagnostics, accurate power monitors, system controllers, and sequencing.
Advanced Power Stages
Advanced power stages can reduce power loss in power supplies by up to one third compared to traditional designs. The latest products take advantage of industry-leading MOSFET technology such as that shown in Figure 1. Here, semiconductor technology with significantly higher power density than was previously possible is combined with advanced packaging that exhibits nearly zero package resistance and inductance and delivers the industry’s lowest industry thermal impedance.
Compared to standard plastic discrete packages, the metal can construction of these benchmark MOSFETs enables dual-sided cooling to effectively double the current handling capacity of high frequency DC-DC buck converters. This dramatically cuts energy losses while shrinking the design footprint of the circuit board. By using driver ICs with innovative control schemes that have been co-designed with (and optimized for) these efficient MOSFET power devices, engineers can obtain the best possible combination of efficiency and electrical performance. In the case of servers, for example, using this technology has been shown to improve efficiency by five to six percent over time.
Advanced Power Systems
Advanced power systems can have an even larger impact on the load’s power dissipation. High power loads such as microprocessors and memory banks have a very unpredictable power profile due to rapid changes in their required performance and function. Under severe requirements these loads can exceed their thermal limits and, therefore, require a stepping back in performance to allow the silicon and the package to cool. Once sufficiently cooled, the load must increase once more. This creates highly inefficient “stop; start” thermal and power cycles.
Permitting high performance silicon to thermal and power cycle wastes both energy and performance. However, by dynamically monitoring instantaneous power, recording its trends over time, and understanding the thermal impedance of the load, it is possible for the power system to accurately predict thermals in the system at any point. With this information, the system can then alter the load’s electrical characteristics (e.g. dynamically change core voltage or reduce clock speed) to limit its power and establish the correct cooling conditions in advance. Energy-efficient advanced variable speed motion control, for example, can be used to guarantee that the load never leaves its required thermal envelope, optimizing its throughput, and hence its performance. This can eliminate up to 15 to 20 percent of total power dissipation.
Application Example
The impact on efficiencies of applying the latest integrated power management semiconductor technologies can be illustrated by considering the server technologies employed in the modern data center. Thanks to their modularity, low cost and small size, these will typically be rack-mounted ‘blade servers’.
By adding racks containing high density blades data center capacity can be increased in line with processing requirements. However, with the latest blades having up to four processors per boards (plus other high performance semiconductors including memory) their power requirements and heat dissipation are both significant. In practice, therefore, data centers often leave slots empty to provide more cooling and keep systems within thermal specifications.
Fortunately, the availability of the latest generation of power semiconductor technologies is helping engineers to address this problem. The two methods discussed in this article, for example, can help reduce the total power consumed in the blade. This reduces the cooling requirements, and thus allows greater blade density in the rack.
The first method allows engineers to develop highly-efficient on-board power supplies. Approximately 80 percent of the power drawn by the blade is consumed through the on-board power supplies, so the efficiency of the power supplies has a large impact on system efficiency. Much of this power is consumed through the microprocessors and memory. For example, a typical high-performance microprocessor will consume 130A at 1.1V, or 146W. Today it is typical for on-board power supplies to have about 80 percent efficiency, or 20 percent losses.
With advanced power control and conversion technology, such as International Rectifier’s XPhase scalable multi-phase architecture (Figure 2) and DirectFET MOSFETs, it is possible to increase system efficiency to over 88 percent. This reduces the power supply’s power loss by 40 percent (from 20 percent to 12 percent). International Rectifier has also developed a family of accurate real-time power monitoring ICs. These facilitate further efficiency improvements by allowing engineers to develop advanced power systems that reduce dynamic power loss in the blade
Conclusion
The cost of employing the advanced power management technologies such as those described above is significantly less than the savings generated. Furthermore, these approaches offer secondary benefits. For instance, with less heat to distribute board level fans can run slower, thus saving more energy and reducing acoustic noise. Indeed, it is estimated that the adoption of optimized power management systems that incorporate advanced power stages, accurate and dynamic power monitoring, and high-performance power controllers will contribute to reductions of up to 25 percent of data centre power dissipation in as little as three years.
Click here for Illustrations:
Figure 1
