LC Filter Design With MLCCs: Why The Applied Voltage Matters

ANP062

The demand for ever more compact electronic circuits (such as switching power supplies) has effects not only on the choice of active components, but also on the choice of passive components for the associated filter system to damp interference. The opportunities that exist today for discrete design thanks to ever-smaller casings also demand smaller discrete filter components. LC filters, for example, often used to be constructed using aluminum electrolytic capacitors because these offer a very wide range of capacitance values. This advantage, however, is becoming increasingly small, as advances in ceramic capacitor technology have enabled the production of high-capacitance SMD ceramic capacitors (multilayer ceramic chip capacitors – MLCCs).

This can be a massive advantage in terms of space, but it also has its drawbacks. Therefore, this application note takes a closer look at the considerable influence of DC voltage on the capacitor, and hence the filter design. The focus is on an LC low-pass filter, as used as an input or output filter for switching regulators or a power supply filter for a module.

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