How does capacitor ESR affect decoupling performance?

Question

I often see discussions about choosing the right decoupling capacitor values, but I’ve also read that the ESR (Equivalent Series Resistance) of a capacitor plays an important role in how effective it is.

How exactly does ESR affect the performance of a decoupling capacitor in power supply filtering and noise suppression?

Are there cases where low ESR capacitors are always preferred, or can higher ESR sometimes be beneficial? What are the best practices for considering ESR when selecting capacitors for decoupling in digital or analog circuits?

Amelia · Answer

ESR (Equivalent Series Resistance) plays a big role in how effective a decoupling capacitor is. Low ESR capacitors, like ceramics, are great at handling high-frequency noise and fast transients, which is why they’re used near IC power pins.

However, ultra-low ESR isn’t always ideal—some regulators actually require a certain ESR range for stability, and higher ESR capacitors (like electrolytics) can help by damping resonances and providing bulk decoupling at lower frequencies.

The best practice is to use a mix: low ESR ceramics for high-frequency suppression, and higher ESR electrolytics or tantalums for bulk energy storage and damping, while always checking the regulator’s ESR requirements in its datasheet.