Choosing the Right Capacitor for Power Supply Decoupling

The Role of Decoupling Capacitors

Decoupling capacitors act as tiny local energy reservoirs for Integrated Circuits (ICs). When an IC suddenly switches logic states, it draws a spike of current. A decoupling capacitor placed close to the power pin supplies this current instantly, preventing voltage droops on the main power rail.

Ceramic Capacitors (MLCCs)

Ceramic capacitors have extremely low Equivalent Series Resistance (ESR) and ESL, making them perfect for filtering high-frequency noise. A typical value is 100nF (0.1uF) placed directly at each IC power pin.

Electrolytic and Tantalum

Electrolytic and tantalum capacitors are used for bulk decoupling. They have larger capacitance values (10uF to 1000uF) and filter out low-frequency fluctuations from the power supply. They are usually placed where power enters the PCB.