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Tantalum capacitors bank on reliability

Posted: 03 Mar 2008 ?? ?Print Version ?Bookmark and Share

Keywords:wet tantalum capacitors? high-reliability markets? polymer tantalum chip capacitor?

While the bulk of demand for tantalum capacitors comes from the handheld and gaming markets, as designers cram greater functionality into these ever-shrinking devices, there has also been quite a bit of activity in high-reliability marketsincluding military, automotive and medicalthat require higher-performance components.

These specialty-type capacitors typically use higher-performance technologies, enhanced manufacturing processes and/or unique construction to deliver higher voltage, higher capacitance/voltage (C/V) values, wider operating temperature ranges and, in some cases, ultralow equivalent series resistance (ESR).

What separates commercial from high-reliability parts is the amount of burn-in and other testing that is performed, said Chris Reynolds, technical marketing manager for AVX Corp. Within the high-reliability category, Reynolds said, are subcategories of reliability testing, including military specification qualification, commercial off-the-shelf (COTS) plus, industrial- or automotive-grade screening, and test levels beyond mil-spec for space- and medical-grade applications. Additional tests can include surge-voltage or surge-current tests, leakage-current screening and 40hr burn-in but without mil-spec qualification, all depending on the application.

Powerful device
In November 2007, Kemet Corp. claimed the industry's first 35V-rated surface-mount polymer tantalum chip capacitor. Traditionally, according to Kemet, such devices have been most commonly used in 14V or lower applications and were limited to voltage applications that did not exceed 20V of continuous duty. Thanks to advancements in materials and manufacturing processes, Kemet said it has qualified the first polymer tantalum capacitors suitable for applications of up to 28V of continuous duty. In addition, the devices have demonstrated surge-voltage-handling capabilities in excess of 46V. The increase in voltage rating now provides designers working with higher-voltage applications, such as 24V and 28V power-input rails, with the option of incorporating polymer tantalum technology into their designs, Kemet said.

Kemet's T521 series initially offers a low-profile "V" case size (7.3mm x 4.3mm x 1.9mm) with a capacitance rating of 15?F and maximum ESR rating of 100m. Future releases will include greater case heights (7.3mm x 4.3mm x 3mm) with target capacitance values of 22?F and 33?F, as well as smaller footprints (3.5mm x 2.8mm x 2mm) targeting application voltages of 6.8?F and lower.

The T521 devices are rated to 125C. Recommended deratings for the series include a 20 percent voltage derating for optimal reliability. For applications exceeding 105C, an additional temperature derating is also recommended. Above 105C, the voltage should be linearly derated to 2/3 the rated voltage for operation at 125C, Kemet said.

Vishay's HE3 wet tantalum high-energy capacitor delivers ultrahigh capacitance and ultralow ESR.

Intelligent chips
An interesting product for many designers is the HE3 high-energy capacitor from Vishay Intertechnology. Introduced in 2H 07, the wet tantalum, high-energy-capacity product is said to offer the highest capacitance of any similar device on the market. The capacitor features a unique case design and the company's SuperTan cathode technology for higher reliability and optimal performance in high-energy applications. Optimized for energy-storage and pulse-power applications in high-reliability avionics and military devices, the HE3 is manufactured to withstand high stress and hazardous environments. A unique double seal is said to provide added reliability and performance.

By combining Vishay's SuperTan hybrid cathode technology with what the company claims are industry-leading anode designs, the HE3 achieves a capacitance range of 3,300-72,000?F and exhibits ESR of 0.035 at 25C and 1kHz. The capacitor offers a 20 percent standard capacitance tolerance at 120Hz and 25C, with tolerances of 10 percent available. The operating temperature range is -55C to 85C.

Vishay also released its Tantamount Hi-Rel COTS T97 series of solid tantalum chip capacitors last year, offering high-reliability screening and surge-current testing options in devices with extremely low ESR performance. Vishay said the caps offer designers a wide array of ratings. Featuring dual-anode construction to minimize ESR, the T97 capacitors are designed for safety-critical applications such as those found in the military, aerospace and medical industries. The parts offer a capacitance range of 22-1,500?F with a voltage range of 4V to 50V. ESR values range from 0.015 to 0.17 at 25C and 100kHz. Devices in the T97 series operate over a temperature range of -55C to 125C. High-reliability screening options offered for the conformal-coated capacitors include Weibull grading and surge-current testing in accordance with MIL-PRF-55365 in a wide variety of case sizes.

High stability
In the area of embedded control systems, AVX offers the TPS and TPM series of tantalum capacitors. They can be used in industrial, telecommunications and other applications that call for long operation and highly stable parameters. The TPS and TPM are said to offer improved filtering capability and power rating within a small package and a reduced height. The mirror-design, multi-anode tantalum caps in the TPM D-case size with a 2.9mm height provide almost an identical ESR level to traditional, E-case multi-anode construction. In addition, because of the higher power dissipation of the D-case, the capacitor can handle higher ripple current than the single-anode design.

The symmetrical design of two horizontal anodes allows the reduction of inductance down to 1nH, which is 50 percent lower than with standard single-anode construction, according to AVX. The lower equivalent series inductance shifts the resonance frequency up to 500kHz, which is said to enable more-effective usage in today's popular switching frequency range of 250-500kHz.

With their high stability and high reliability, AVX's TPS and TPM series of tantalum capacitors suit embedded control system applications.

Automotive ICs
For automotive applications, Vishay offers the TH3 molded solid tantalum chip capacitors, which are designed to provide high reliability with a high-temperature capability of 150C with 50 percent voltage derating. By providing higher temperature capabilities than the industry-standard 125C, the TH3 capacitors give designers a less expensive option for high-temperature applications, said Vishay. Although Vishay's TH3 molded solid tantalum chip capacitors are optimized for a variety of high-temperature automotive uses, including under-the-hood and on-engine applications--such as engine control, fuel injection systems, steer-by-wire, diesel ignition control and transmission control--they are also finding homes in sensor applications such as for tire pressure monitoring and temperature control, and in industrial applications related to the control of high-temperature materials and oil exploration sensing systems.

AVX also offers the THJ series, with a higher temperature range of up to 175C for automotive under-the-hood or downhole drilling applications. "The biggest concern in automotive is temperature swings over time. The amount of temperature cycling stress in under-the-hood applications means you need parts that are good at handling those temperature extremes," said Reynolds.

- Gina Roos
eeProductCenter




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