Electronics

The market demand for solutions with higher bulk capacitance and lower ESR continues in both commercial and established reliability applications is continuing. These solutions require increased volumetric efficiency as well as reduced real estate / payload.

In established reliability applications, the voltage requirements within aerospace and avionics have remained fairly stable as common bus voltages from 5V to 28V. However, as system integration includes more high speed CPUs and ASICs or data processing, there is an increasing trend towards low voltage applications that require regulated power in the 1.5V to 3.3V range.

For low ESR applications a new series recently incorporated into MIL-PRF-55365 was the CWR29 family. These include a very wide range of CV options up to 50V rated, with Weibull reliability grading and optional surge current test. The typical ESR performance of these parts is usually well within specification; for example the 330uF/6V rating noted above will have a maximum limit of 180 mΩ, but typical performance well under 100mΩ.

Having optimized the characteristics of discrete capacitors in medium power applications, it is sometimes necessary to use a bank of capacitors in parallel, or a parallel/series configuration of capacitors to reach the ESR target, capacitance and required voltage derating of some higher voltage bus lines (for example 28V), or where the derating rules are conservative. A new series of parts that allows this is the stacked tantalum module. These can be configured in standard 2, 4, or 6 unit stacks with other custom configurations available. The advantage of using such stacks is that the manufacturer can use parts within set ESR limits and, matching the ESR in a stack, ensures that current sharing is better equalized. From the design perspective, this advantage gives a large reduction in real-estate with better packing density on the PCB and therefore improves system volumetric efficiency.

Given the emphasis on testing and reliability, tantalum chip capacitors have an excellent track record in avionic and space applications, but the typical failure mechanism remains shortcircuit. For additional safety, there is a new series being introduced that includes a Weibullgrade reliability internal element matched to an internal fast-acting fuse. This gives the best of both options – established reliability performance and failsafe operation. It is offered as both a discrete capacitor and in module format (and all with standard dimensions). In the module version, each element is independently fused so in the event an element failure, there is still redundancy in the system.

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