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An Accurate Method For Measuring Capacitor ESL

The equivalent series inductance (ESL) of chip capacitors is becoming an increasingly important parameter as bandwidths and switching frequencies rise in many high-performance systems. The stability and high-frequency dynamic performance of these systems is dependent, in part, on capacitor ESL. For their part, manufacturers of ceramic and tantalum capacitors have been working hard to reduce the ESL of their components. However, system designers cannot simply rely on the capacitor vendors’ published data for ESL, which is limited at best. It’s important that designers be able to make their own ESL measurements.

With ESL values typically in the range of 1 nH to 5 nH, measuring the ESL of chip capacitors is not a trivial task. At present, some designers try to measure ESL by measuring the resonant frequency of the capacitor, and calculating inductance from that reading. Unfortunately, such measurements are often inaccurate because of the parasitic inductance in the test setups or lack of probe and adapter calibration. Perhaps it’s no wonder that most designers simply don’t bother to measure ESL at all.

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