A New, Low ESR Fused Solid Tantalum Capacitor

Solid tantalum capacitors are extremely reliable due to the nature of their materials and construction. The construction allows for small DC leakage sites within the device to become isolated electrochemically and thereby insignificant.

Tantalum capacitors can accommodate a variety of environmental conditions such as temperature, humidity, shock, vibration, mechanical and electrical stress, including applied voltage, current, ripple current, transient current and voltage. However, when using solid tantalum capacitors, application guidelines must be followed to insure that the full reliability of the capacitor is realized.

Due to their inherent reliability tantalum capacitors are increasingly utilized in harsh applications. When application guidelines can be exceeded, such as transient conditions, there is the concern that the device could fail, over heat and potentially burn. This concern primarily centers on high voltage product where there is sufficient energy to overcome its natural self-healing properties.

There are commercially available fused tantalum products that provide protection for these rare events by causing the device to “open” when drawing elevated currents. These fused devices utilize a bi-metallic fuse wire. The single wire fuse limits flexibility in design and can increase the Equivalent Series Resistance (ESR) of the complete package 2 fold or more compared to the capacitor itself.

A new style fused solid tantalum capacitor has been designed that incorporates an internal thin-film fuse which provides safety, consistency, reliability, ultra-fast fusing, compactness and a lower ESR product than commercially available fused solid tantalum capacitor product today. The design allows for flexibility in specifying fuse characteristics and/or targeting ESR levels that more directly fit the application, while not sacrificing levels of capacitance available in the case. The availability of fuses with a wide current range and response times allows for specific circuit protection to be designed in.

The configuration of the construction of this device also allows for compliance with the low impedance requirement of MIL-PRF-55365 Weibull grading.

This paper reviews the design, construction and characterization data for this product.