Power Management
A new era of energy optimisation
Patrick Le Fèvre looks at how the Information and Technology industry can significantly reduce energy consumption in its key applications by using a dynamic bus voltage architecture
D
ynamic Bus Voltage (DBV) technology is being seen as one of the most significant technological
breakthroughs for the Information and Communications Technology (ICT) industry. System designers are seeking to reduce energy usage at the board level and the introduction of low-power-consuming silicon devices alone will not be enough to effectively limit the energy requirements of modern networks. However, the latest board-power-consumption monitoring and control technologies can produce energy savings of between 3 and 10 percent at board level with the use of advanced Dynamic Bus Voltage (DBV) architectures. The benefits become increasingly obvious when saving 1W at the board level results in an average saving of 2 to 3W at the system level.
The world is becoming increasingly dependent upon ICT with demand growing for more online services, faster networking, increased data processing and data storage capabilities and this demand is driving the growth of ICT equipment in computing-intensive environments, including the setup and expansion of huge datacenters. There are strong environmental
concerns over the impact of data- processing facilities - the European Commission DG INFSO (Directorate General - Information Society) report, published in September 2008, estimated that European telecoms operators could see their overall network energy requirement reach 35.8TWh by 2020. The nature of wide-area
communications networks involves massive amounts of parallel processing to simultaneously route arbitrary numbers of subscribers and widely varying network traffic levels; and users expect almost flawless communications across global networks. As a result, datacom and telecom processing racks will house multiple instances of similar circuit boards -
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some of which are redundant elements to guard against hardware failures.
Intermediate Bus Architecture The power architecture increasingly being used in the ICT industry is the Intermediate Bus Architecture (IBA), adopted as the standard in 2003. The IBA model differs from the classic Distributed Power Architecture (DPA), which typically comprised a number of isolated DC/DC converters on each board that down- convert the 48 VDC line to values that suit the load circuitry, daisy-chaining additional regulators for expediency. The IBA uses Intermediate Bus Converters (IBCs) to convert a traditional 48 VDC distribution-level power line used in data/telecoms to a typically static 12 VDC. This first ‘down-conversion’ 12V level feeds a number of non-isolated DC/DC Point-of-Load (POL) regulators, which supply the final load voltages at IC logic supply levels of 3V or below (see Figure 1).
the power envelope to meet load conditions. It does this by adjusting the previously fixed 12 VDC intermediate bus voltage via the use of advanced digital power control and optimised hardware – the Advanced Bus Converter – combined with an energy-optimiser series of algorithms. This can lead to a reduction in both energy consumption and power dissipation, which in turn contributes to a reduction in required cooling.
standalone to sophisticated systems, each being able to monitor and fine tune their performance in real time – including the value of their intermediate bus voltage.
DBV in practice
The advanced digital converter offers on- the-fly programmability and quickly responds to commands that span simple output-voltage adjustments to complex operations such as trimming the values of the digital filter that characterises control- loop responses.
Figure 2: Experimental dynamic bus voltage combining analogue DC/DC and potentiometer
Figure 1: Intermediate Bus Architecture with 12V bus voltage and POL regulators
The use of two down-conversion stages
offers the opportunity to achieve optimal balance between the intermediate bus voltage that supplies the POLs and the load currents supplied by the POLs at any particular time. This is crucial for maximising power-conversion efficiency at the system level. The choice of 12 VDC was made to ensure high enough voltage to deliver all the power required by the board, or load, in times of high network data traffic. This approach can become highly inefficient when there is low traffic demand.
Dynamic Bus Voltage The Dynamic Bus Voltage is an evolution of the Intermediate Bus Architecture – it provides the ability to dynamically adjust
Components in Electronics
Intended for non-static loads, DBV implies the need for tightly coupled supervisory measurement and control and intelligent devices that can operate autonomously or as part of a network. While it is possible to implement these requirements using analogue technology, it comes at significant expense in terms of PCB area and component count.
In addition, it also becomes cost
effective to include a measurement and control system together with a communications interface alongside the DC/DC controller, when implemented in an advanced mixed- signal process technology. Adopting industry-standard PMBus protocols enables a simple serial interface to communicate with compatible board-level devices using a standard command language that is specifically designed for power control applications. The advent of commercially
Implementing dynamic bus control in telecoms equipment requires the writing of application code to supervise the system: making judgments regarding when to increase or decrease the intermediate bus voltage with rising and falling load levels. Refining algorithms to make reliable decisions take some effort, as it is can be difficult to visualise the complex series of interactions created by a combination of IBCs and POL regulators. Before considering the implementation of DBV technology, it is important to validate the potential energy savings by modelling a typical system and verifying that the model is both accurate and reliable in a real application. The starting point involves exercising each IBC and POL in a system over at least the range of input voltages and output currents that it will experience in the end application and recording the power losses that result at each step. Plotting these parameters against one another creates a three- dimensional graphical overview of each device’s performance over the chosen measurement area (see Figure 3).
Figure 3: Graphing power losses resulting from setting a digitally controlled POL to 1.0Vdc output and ramping the load from zero to 20A, while stepping the input level from 4.5 to 14Vdc
produced digital power-converter modules allows systems architects to slash implementation complexity while supporting applications that range from
Consisting of the test results at each step, the array of data points that build the graph is also useful as input data for simulation. Evaluating the test results for
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