Power
are also prevented from passing through the converter, improving reliability and reducing peak voltage rating requirements of the PoLs.
System considerations are important Headline goals in a rack power architecture are high conversion efficiency and power density, but a ‘holistic’ view should also be taken: active cooling, for example, is a major cost, consuming power itself and if the main system dissipation is in converters on blades, the route for heat extraction has to be considered. Low profile bus converters optimized for top- side cooling are advantageous in this respect, allowing heat extraction through attached cold-plates or heatsinks with blown air or even liquid cooling.
Losses in interconnections can be substantial at higher power and initial distribution via bus-bars at 48V is a good compromise between safety, power dissipation and ease of coupling-in battery backup. Close to the end IC loads, currents can be at their highest, often 100A-plus, potentially producing high dissipated power in PCB tracking. Voltage is also dropped if the PoL really isn’t directly at the load so schemes that split the PoL converter power and control stages into separate hardware can be a useful approach. For example, a PWM control IC could be fitted directly under a power-hungry device, sensing and controlling voltage to be very accurate while the power stage might be a module on the top-side of the board, adjacent to the end load.
An optimum architecture design will also include considerations of the continuous, minimum and likely peak loads on power conversion and their durations. Intermediate bus converter and PoLs will have a ‘thermal’ rating for power output, limiting long term dissipation and internal temperature rises, but computing loads can have a high ratio between ‘sleep’, operating and peak power consumption. If these values are known and the different power conversion stages have surge current ratings, the converters can be smaller and lower cost than ones rated
Figure 3: Different arrangements of bus and PoL converters with about the same end-to-end efficiency, but different loss distribution
to supply the peak power continuously. Converters with ‘flat’ efficiency curves down to light loads are also advantageous to leverage the lower system dissipation aims of a load’s sleep or idle modes.
Some example solutions
The Flex Power Modules BMR313 part (Figure 2, left), is an example of a 4:1 ratio, non- isolated and unregulated intermediate bus converter with high peak power capability. It has been developed in co-operation with onsemi and features a continuous power rating of 1kW in an ultra-compact package just 23.4 x 17.8 x 7.65mm in an industry-standard LGA footprint. Peak power capability is however 3kW for an impressive 15kW/in3 surge rating. Input operating range is 40-60VDC for an output of 10-15VDC and comprehensive monitoring, configuration and control is provided through a PMBus interface. Efficiency is 97.3 per cent at 54V input and 40A load.
For lower power systems, the BMR320 (Figure 2, middle) has an 8:1 conversion ratio and again is non-isolated and unregulated. The part is rated at 400W continuous and with its output of 5-7.5VDC for an input of 40- 60VDC, it matches the input of PoL converters optimized for highest efficiency with lower input voltages. An example is the BMR510 (Figure 2, right), which is a 2-phase VRM or integrated power stage, capable of 40A per phase, 80A total. The LGA-format part is just 10 x 9mm footprint, 7.6mm high, is optimized for top-side cooling and incorporates drivers, power stages and magnetics. With a suitable controller, it can output a programmable 0.5 to 1.3VDC. The input range of the BMR510 is 4.75-16V so it can be used with bus converters with higher output voltages with some reduction in efficiency.
With the options to select bus converter ratio and power rating depending on continuous and peak load demands, there is flexibility to optimize efficiency and where
power is dissipated for easiest cooling. Figure 3 shows two scenarios with a BMR313 4:1 bus converter, a BMR320 8:1 bus converter and BMR510 PoL with both scenarios producing the same end-to-end efficiency of about 87 per cent for around 400W total loading. Although the BMR313 is running at well below its continuous rating of 1kW and 3kW peak, peak efficiency occurs at about 400W. The 4:1 solution might be preferable if 12V is anyway required for loads such as PCIe power and dissipates relatively more power in the PoL converter. With the BMR320 at 6V output for 48V input, the BMR510 PoL operates more efficiently, with relatively less power dissipation and relatively more in the bus converter, but this is further away from the end load and perhaps easier to cool. With a 6V bus, the intermediate bus current is higher for the same end load power however, requiring heavier tracking for the same power loss compared with a 12V intermediate bus voltage.
Conclusion
For a ‘small and mighty’ power architecture, bus and PoL converter data sheets from Flex Power Modules can be examined to find the ‘sweet spot’ of loading, voltage conversion combinations and distribution losses, where efficiency peaks. All parts mentioned are also supported by the Flex Power Designer software for quick configuration and evaluation of performance in a chosen application.
Figure 2: High-efficiency bus converters (left, middle) and PoL power stage (right) from Flex Power Modules
www.cieonline.co.uk https://flexpowermodules.com/ Components in Electronics February 2023 47
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62
