Designing a low-cost, reusable power-distribution architecture

-July 08, 2015

The latest, spacecraft sub-systems are baselining advanced semiconductors requiring multiple low-voltage, high-current rails requirements, e.g. FPGAs with core voltages of < 1V@30A. Furthermore, individual loads have unique sequencing, transient, line and load-regulation requirements, which can complicate the design of the power-distribution network.

Current spacecraft busses provide 28 and 100V unregulated power rails, which can be used to generate isolated, regulated supplies efficiently for the latest space-grade semiconductors. To develop a low-cost, scalable, power-distribution architecture to meet the needs of future spacecraft sub-systems, a reusable design is sought which will efficiently generate multiple smaller rails from either an input of 28 or 100V while limiting the total number of power-conversion stages.

Space-grade DC-DC convertors are available that have identical packages, PCB footprints and pin-outs, which allow the first stage of power conversion to be swapped to meet specific mission needs without having to re-engineer the hardware design. This is a key requirement necessary to deliver a low-cost, reusable, scalable, reliable, and efficient power-distribution architecture!

Developing a low-cost, reusable, power-distribution architecture requires looking at the complete design and not just the price of individual components. Some devices contain a converter and the control loop integrated within a single package, requiring only the line voltage. Others need external inductors and capacitors, which adds to the overall cost, area, layout, and design effort. Some DC-DCs contain internal EMI filters while others require the designer to add the necessary passives.

The following diagram compares the relative area of space-grade DC-DCs that can be used to generate an intermediate voltage from either a 28 or 100V bus input. Some offer isolated outputs and several contain internal EMI filters. A number of vendors offer different ranges of qualified, DC-DC convertors based on the power rating, the input voltage, number of outputs, package type, topology, or the level of radiation tolerance.


Figure 1 Here are the relative sizes of competing space-grade DC-DC convertors.

The latest DC-DCs are using zero voltage/current switching techniques to improve conversion efficiency as well as adaptive, feed-forward compensation to account for voltage drops to the load and to avoid signals crossing the isolation barrier.

Some suppliers perform a comprehensive set of radiation testing as part of device qualification including total dose, ELDRS, displacement damage, SEE, and gate rupture to deliver MIL-PRF-38534 components which are MIL-STD-1547 or TOR-compliant.

To meet the supply, regulation and transient current demands of the latest semiconductors, switching or linear point-of-loads (POLs) are used to provide an efficient power-distribution architecture and overcome the large transmission losses associated with a centralised approach.

Many providers of space-grade microelectronics sell qualified POLs offering different power and current ratings, topologies, efficiencies, fixed single, dual bipolar and multiple, adjustable output options with specific line, load, and cross-regulation specifications. Just like DC-DCs, the design of a low-cost, reusable power-distribution architecture requires looking at the complete design and not just the price of individual components. Some POLs contain the converter together with its control loop integrated within a single package, requiring only the intermediate bus voltage as the line input. Others need external inductors and capacitors, which add to the overall cost, area, layout, and design effort. Figure 2 compares the relative area of the latest, space-grade POLs.



Figure 2
This is a comparison of relative sizes of competing space-grade POLs.

To meet the demands of FPGAs, multiple POLs can be connected in parallel to increase the output current rating of the overall DC-DC. For example, Figure 3 shows how two 10A space-grade bucks connected together can provide the 1V core voltage to power a Xilinx V5QV FPGA. Figure 4 shows an integrated product example, which can be configured to output four independent rails rated at 4A or a single supply capable of sourcing 15A at reduced ripple. A smaller, 4A single-output product is also available.


Figure 3 Parallelising two 10A bucks can produce a 20A DC-DC.
Image courtesy of Peregrine Semiconductor


Figure 4 This integrated product example is a quad 4A POL.
Image courtesy of Microsemi Corporation

It is now possible to develop a low-cost, reusable, scalable, reliable, and efficient power-distribution architecture to supply future satellite sub-systems. A diverse range of DC-DCs, switching and linear POLs are available in various topologies to design enabling products.

Until next month, stay regulated and ripple-free!

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