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MLCC Self-Resonant Frequency Calculator
This calculator estimates the self-resonant frequency of an MLCC from capacitance and equivalent series inductance. It is useful for decoupling, RF filtering, high-speed digital design, power rail impedance planning, and capacitor selection.
Input Parameters
Results
Below SRF, the MLCC behaves mainly as a capacitor. Above SRF, ESL dominates and the part behaves more inductively.
Equations Used
Self-Resonant Frequency:
fSRF = 1 / (2π√(L × C))
Angular Resonant Frequency:
ω = 2πf
Capacitive Reactance:
Xc = 1 / (2πfC)
Inductive Reactance:
XL = 2πfL
Minimum Impedance Near SRF:
Zmin ≈ ESR
Where:
C = capacitance in farads
L = equivalent series inductance in henries
ESR = equivalent series resistance in ohms
Frequently Asked Questions (FAQ)
Q1: What is MLCC self-resonant frequency?
It is the frequency where the capacitor's capacitive reactance and equivalent series inductance cancel each other. Around this point, impedance is typically at its minimum.
Q2: Why does SRF matter in decoupling?
A capacitor is most effective near its low-impedance region. Above SRF, the capacitor becomes inductive and may not suppress high-frequency noise as expected.
Q3: What determines MLCC SRF?
SRF is mainly determined by capacitance and equivalent series inductance. Package size, mounting layout, via placement, and PCB geometry can change effective ESL.
Q4: Does ESR affect self-resonant frequency?
ESR has limited effect on the ideal SRF formula, but it strongly affects the minimum impedance and damping near resonance.
Q5: Why do smaller MLCC packages often have higher SRF?
Smaller packages usually have lower ESL and often lower capacitance, both of which can push the self-resonant frequency higher.
Q6: Is calculated SRF the same as datasheet SRF?
Not always. Datasheet SRF depends on measurement fixture, mounting style, actual capacitance under bias, ESR, ESL, and manufacturer test conditions.
