POWER ELECTRONICS
locally converted for each load. Instead, an emerging trend is to handle AC-DC conversion in bulk, perhaps with just one converter system per rack. The resulting DC current is then distributed to each blade. With the growth we see in total rack power requirements, there’s also a trend from 12V DC to 48V DC distribution. By increasing the voltage fourfold, the current needed to deliver the same amount of power can be similarly decreased, reducing losses by a factor of 16 and avoiding the need for large, expensive power cables.
The 48V DC supply to a board is often converted first to 12V by an Intermediate Bus Converter (IBC), and then by a local Point of Load (PoL) converter to the low voltage required by particular components. This two- stage architecture provides high efficiency and can deliver high currents if required, or conversely can provide low currents in a cost-effective system.
Another approach, called direct conversion, uses a single stage to convert the 48V supply voltage directly to the low voltage required by a load, which may well be 2V or less. By keeping the power supply at the higher 48V voltage right up to the load, this can be helpful where high current is required, for example for high-end processors, ASICs and FPGAs. Whether two-stage or direct, today’s DC-DC converters typically include sophisticated digital control, for example via the industry-standard PMBus.
New power devices in practice Let’s look at an example device: the BMR492 from Flex Power Modules. This is a high-power DC-DC converter designed for data center applications, which delivers a 12V output from a nominal 48V input voltage. It can provide a peak output of up to 1100W for short periods of up to a second, making it well-suited to the ‘burst mode’ power demands of modern CPUs, as well as achieving high efficiency of up to 97.4%.
While these figures are impressive, the key step forward with the BMR492 is to deliver such results in a compact package. In fact, it uses the industry-standard ‘eighth-brick’ format (measuring just 58.4 x 22.7 x 13.2mm) – and provides power output and performance previously only possible in larger quarter-brick devices.
One approach for the downstream Point of Load (PoL) is to use a compact, vertically- mounted SIP (single inline package) format, which minimises the board space occupied. For example, the BMR474 from Flex Power Modules is a digital PoL DC-DC converter, which provides an output of between 0.6V and 3.3V, taken from an input in the range 6V to 15V. Efficiency is 95.1 % at full load, with 12V input voltage and 3.3V output. With its vertical SIP mount design, the BMR474 has a small footprint of only 2.84cm2, thus using a minimum of board space. It can still deliver up to 80A of output current to meet the needs of typical data center loads. As well as their excellent electrical
Figure 3: Example screenshots from Flex Power Designer
specifications, the BMR492 and BMR474 offer superior thermal behavior, with options for conduction or convection cooling, as well as robust over-temperature protection. Design engineers can optimise both electrical and thermal performance by using Flex Power Designer (FPD), a free software tool. Data center performance is climbing, but at the same time, systems are becoming more compact, while demands for 24x7 uptime and growing security threats create their
challenges. All the while, there are downward pressures on electricity consumption. For power system design engineers, this may at first appear an unassailable feat. But new architectures and components are here to help resolve design challenges – ensuring our ever-growing demand for cloud services can be met.
Flex Power Modules
www.flexpowermodules.com
JULY/AUGUST 2021 | ELECTRONICS TODAY 45
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