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Low Resistance Tantalums are a Match for Anyone
Electronics Weekly -- Electronic News, 6/13/2002


While the future of the tantalum capacitor must come to terms with supply and human rights issues, right now it is still the capacitor of choice for decoupling power circuits. The latest tantalums are even matching the low equivalent series resistance (ESR) performance of aluminum electrolytics.

Like most suppliers, Germany-based Epcos AG has not shifted its R&D focus from tantalums. It recently introduced tantalum chip capacitors with polymer multi-anodes, which offer low ESR. Epcos is the successor company of Siemens Matsushita Components, the former joint venture of Siemens AG and Matsushita.

The multi-anode design of these surface mount devices in case size E (7.3mm by 4.3mm by 4.1mm) comprises three low-profile polymer-coated tantalum anodes connected in parallel. According to the supplier, this reduces ESR to one-ninth of that of conventional tantalum capacitors, so that ESR values in the region of 10mohm are obtained. Single-digit ESR will become feasible in the medium term, the company said.

Epcos will soon be able to offer capacitors with a capacitance up to 1000uF for a rated voltage of 4V. A further increase to 1500uF and beyond is planned for next year.

The aim of the low ESR polymer multi-anode design is to offer tantalums that can be used as single device alternatives to using OSCON, aluminum electrolytic or ceramic capacitors connected in parallel.

Samples of tantalum polymer capacitors rated at 680uF/4V are available from Epcos. A type rated at 470uF/6.3V is in preparation. ESR for both types is in the region of 10mohm. The company also has a capacitor rated at 1000uF/4V whose ESR will likewise be in the 10mohm region.

To push the ESR even lower you must also replace the traditional MnO2 cathode with a conductive polymer cathode.

Some of the lowest ESR tantalums on the market come from suppliers NIC and Kemet Corp., which have both recently introduced ranges of tantalum electrolytic capacitors with conductive polymer cathodes instead of the traditional manganese oxide (MnO2) cathodes.

Greenville, S.C.-based Kemet has combined a multiple anode design with a conductive polymer cathode to create a 1000uF chip capacitor with typical ESR below 7milliohms

In comparison, some of the lowest ESR aluminum electrolytics on the market are available from NIC whose NSP series of surface mount capacitors are based on a polymer solid electrolyte to offer low ESR and high ripple current ratings at high frequency. With a capacitance range up to 390uF, ESR specifications are down at 12mohm. Ripple current ratings have also increased to up to 3000mA (rms) (100kHz, +105 deg C).  [ www.lowESR.com ]

According to the supplier, the solid polymer electrolyte also improves life expectancy of the device.

AVX Corp. has stuck with MnO2 technology with tantalum dielectric in its latest TPS III series, which is specified up to 125 degrees Celsius, higher than competing technologies.

According to Myrtle Beach, S.C.-based AVX, when MnO2 is used as the counter-electrode material in tantalum capacitors, its conductivity increases as temperature increases. This results in lower ESR at elevated temperatures.

The minimum achievable ESR value is 40mohm and ripple current values as high as 2.5A(rms).