PDN Target Impedance & Capacitor Estimate
Translate a load step and droop budget into target impedance and ideal capacitance.
Live results
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Formula and worked example
Method. Target impedance = allowable ripple ÷ load step. Ideal capacitance = load step × hold-up interval ÷ allowable capacitive droop.
Assumptions. Ideal constant-current load step. ESR creates an immediate voltage step. ESL and mounting inductance raise high-frequency impedance. Account for voltage derating and validate across frequency.
Example. A 2 A step with 50 mV ripple gives 25 mΩ. Holding 2 A for 10 µs with 50 mV droop needs 400 µF ideally.