Decoupling Capacitor Calculator
Decoupling that's undersized shows up as brownouts and glitches the moment a board sees a real current transient; oversized decoupling just wastes board space and money. This selector works from a target power-rail impedance and the bulk charge reservoir a load actually needs, so bypass and bulk capacitance get sized with a number behind them instead of a rule of thumb copied from the last design.
Decoupling Capacitor Selector
Target impedance and bulk charge reservoir
Show your work
Required capacitance
15.9 nF
Nearest E12 value
15.0 nF
Self-resonant frequency
39.9 MHz
Z from ESL alone at f
628 mΩ
Bulk / transient reservoir
Bulk capacitance (C = I·Δt / ΔV)
20.0 nF
Above the self-resonant frequency the part is inductive and stops decoupling — that impedance figure is set by loop inductance, not by capacitance. Shorten the via-to-pad loop before adding more capacitors.