Decoupling Capacitor Calculator

Decoupling capacitors provide a local reservoir of charge near the IC to supply instantaneous current during switching transitions. They reduce power supply noise and maintain stable voltage levels by bypassing high-frequency current demands around the power distribution network.

Typically use 2-3 capacitors per IC: one small high-frequency capacitor (100nF-1μF) placed very close to the power pins, and one larger low-frequency capacitor (10μF-100μF) for bulk energy storage. Complex ICs may require additional capacitors.

Decoupling and bypass capacitors serve the same function - they are often used interchangeably. Both provide local energy storage and filter high-frequency noise from the power supply to ensure clean power delivery to ICs.

Place high-frequency decoupling capacitors as close as possible to the IC power pins, ideally within 5mm. The closer the placement, the lower the loop inductance and the more effective the capacitor at high frequencies.

Different capacitor values target different frequency ranges. Small capacitors (100nF) are effective at high frequencies but have limited charge storage. Large capacitors (10μF+) store more energy but are less effective at high frequencies due to parasitic inductance.

Too little capacitance can cause power supply noise, logic errors, and EMI issues. Too much capacitance wastes board space and cost, and can cause power supply startup issues or create resonances that amplify noise at certain frequencies.

Use X7R ceramic capacitors for decoupling applications. X7R maintains stable capacitance over temperature and voltage variations. Y5V capacitors can lose up to 80% of their capacitance under bias voltage, making them unsuitable for critical decoupling applications.

Trace inductance between the capacitor and IC reduces decoupling effectiveness at high frequencies. Keep traces short and wide, use vias to minimize inductance, and consider placing capacitors on the same layer as the IC when possible.