Decoupling Capacitor Placement Calculator

Small capacitors placed near a chip's power pins filter out electrical noise and keep voltage stable — the Decoupling Capacitor Placement Calculator tells you exactly what values to use and how many to place. Select your application type (MCU, Op-Amp, RF, etc.) and enter your supply voltage, supply current, target frequency, target impedance, and PCB trace length to get your primary capacitor value, secondary and bulk capacitor values, effective impedance, maximum trace length, and recommended total capacitor count.

V
A
Hz

Frequency of noise you want to filter

Ω

Lower impedance provides better filtering

%
Hz

For switching power supplies

mm

Distance from capacitor to IC power pin

Results

Primary Capacitor Value

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Secondary Capacitor

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Bulk Capacitor

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Effective Impedance

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Max Trace Length

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Recommended Cap Count

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Results Table

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Frequently Asked Questions

Why use multiple capacitor values for decoupling?

Different capacitor values are effective at different frequencies. Large capacitors (10-100µF) handle low frequency noise and power transients, while small capacitors (10-100nF) filter high frequency switching noise. Using multiple values creates a broader frequency response.

What's the difference between X7R and C0G capacitor types?

C0G (NP0) capacitors have excellent stability and low losses but limited to smaller values. X7R capacitors offer higher capacitance values but have more variation with temperature and voltage. For critical decoupling, C0G is preferred for small values, X7R for larger ones.

How close should decoupling caps be to the IC?

Decoupling capacitors should be placed as close as possible to the power pins, ideally within 5mm. The trace length creates inductance that reduces filtering effectiveness at high frequencies. Via placement should also minimize loop area.

How do I choose capacitor values for different frequencies?

Use the formula C = 1/(2π × f × Z) where f is the target frequency and Z is desired impedance. For digital circuits, start with 100nF for frequencies around 100MHz and add larger values (1-10µF) for lower frequency filtering.

What are the placement strategies for different power plane configurations?

For solid power planes, place capacitors near IC power pins with short vias. For split planes, add extra capacitors at plane boundaries. Multi-layer boards allow better power distribution, reducing the number of capacitors needed compared to 2-layer designs.

How many decoupling capacitors do I need per IC?

Generally, use one 100nF ceramic capacitor per power pin pair, plus one larger bulk capacitor (1-10µF) per IC. High-speed or high-current ICs may require additional capacitors of different values to cover a broader frequency range.

What happens if I don't use enough decoupling capacitors?

Insufficient decoupling can cause power supply noise, signal integrity issues, increased EMI, and circuit malfunction. Digital circuits may experience timing errors, while analog circuits can suffer from reduced performance and increased noise.

Should I use different capacitor packages for decoupling?

Smaller packages (0402, 0603) have lower parasitic inductance and are better for high-frequency decoupling. Larger packages (0805, 1206) can handle higher currents and voltages. Choose based on frequency requirements and current handling needs.