­Solutions for Data-Centres and Other High-Power Applications

Data centres are major consumers of the power that we generate. According to Cirkla, in 2022 there were over 8,000 data-centres around the world. On average, each data-centre consumes as much energy as 25,000 homes, and combined, their usage is around 1% of global energy consumption. As the IoT and AI gain more influence in our lives, the amount of energy usage by datacentres is only set to increase, with some forecasts saying that it could double in the not too distant future. It has also been estimated that only 40% of that energy consumption is used for computing purposes, with the majority of the remainder being used to combat heat generation. Designing more efficient power architectures would help with creating less heat through reducing inefficiency and therefore cutting the need for cooling.

It is not just data-centres that would benefit from more efficient architectures at higher power levels, the same requirements of delivering currents from 100A to over 1000A efficiently by packages small enough to be situated near the processor to reduce resistive losses are desirable for many other applications, such as powering high-performance computing clusters, and even single components, such as high-end FPGAs or AI processors.

Traditionally, processors in data-centres are powered by a two-stage process. The voltage is converted from the 48V or 54V supply to an intermediate value by a device such as Analog Devices’ LTM4660 60V hybrid µModule, which can deliver a conversion efficiency of up to 97%. However, in applications like this, the efficiency can drop off at higher currents. That intermediate voltage is then down-converted to one or more point-of-load voltages by solutions like the Analog Devices’ LTM4681 quad-31.25A/single-125A stepdown μModule. The LTM4681 uses a similar multi-phase approach to a buck regulator, allowing it to generate four different voltages of between 0.5V and 3.3V if required. For higher current applications, two outputs can be tied together for a 60A output, leaving two outputs free for other tasks, such as supplying the I/O. Alternatively, for even higher power, all four outputs can be combined to output 125A, or 4 of the devices can be paralleled together for loads of up to 500A. It is possible for the LTM4681 to reach efficiencies of around 94%, but as the output voltage drops below 1V, that efficiency can fall due to I²R losses.

The drawback to this type of architecture is that although the two converters are very efficient by themselves, their losses compound. For example, two 90% conversions would give a total conversion efficiency of 81%, and at high currents and low voltages, those can be realistic figures. That means almost a fifth of the available power can be wasted as heat. As processor core voltages continue to drop, greater efficiency losses can be expected in the future with two-stage conversions. A single-stage conversion should theoretically improve this, but until fairly recently a direct conversion from 54V/48V to under 1V was very hard to achieve with the efficiency and precision that these applications require.

However, that is changing as direct conversion modules have recently been developed and are now available on the market. Analog Devices used the recent Embedded World exhibition in Nuremberg to demonstrate its own single step conversion modules intended for data-centres and similar applications. The company’s LTP880x family can convert input voltages from 45V – 65V down to output voltages of 0.5V – 1V at currents of up to 200A.

Figure 1, An architecture with a single-stage conversion from 48/54V to the processor core

Talking about the new range, Frederik Dostal, Subject Matter Expert, Power Management at Analog Devices said, “The LTP8800-4A can provide a total conversion efficiency of above 90% at 100A and around 87% efficiency at 200A, which is considerably higher than any two stage conversion can offer in the same conditions. It is tiny device of only 22mm x 24mm x 22mm, but it can dissipate heat generated into the air rather than onto the PCB, which helps a lot as the processor is already heating the circuit board. The device can often be used on the opposite side of the PCB from the processor, which allows the heat to be distributed more evenly. Paralleling outputs is easily to achieve higher levels of power. For example, Analog Devices has launched a demonstration board that can use up to ten LTP8800 for applications that require over 1kA”.

Figure 2, The high-power demonstration board can combine the outputs from ten LTP8800 devices to power applications up to 1kA

www.analog.com