PDN Basics – Paralleling Tantalum and Ceramic Capacitors Can Be Risky
Because of their high ESL compared to ceramic, tantalum capacitors are not the optimum choice for high frequency decoupling. Paralleling tantalum capacitors for bulk capacitance and ceramic for high frequency decoupling. By evaluating performance we can determine the best combination of capacitor type and values to achieve high-frequency decoupling.
Tantalum capacitors provide high capacitance for a given size though they have higher ESL than ceramic and are, therefore, not the optimum choice for high frequency decoupling. The common solution is to parallel tantalum capacitors for bulk capacitance and ceramic for high frequency decoupling. A popular rule of thumb is to parallel ceramic capacitors of different values, such as 0.1 uF, 0.01 uF and 0.001 uF to provide wideband decoupling. In theory, this sounds like an ideal solution but in practice, it can lead to disastrous results.
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