Voltage Droop Calculator

Work out voltage droop instantly with clear inputs, formula shown and shareable results.

About Voltage Droop Calculator

Supply droop has two parts: L di/dt from the power delivery inductance and I x Z from the resistive impedance of the decoupling network. A 25 A step in 2 ns through 120 pH gives 1.5 V of inductive droop unless on-die capacitance supplies the transient locally.

Formula

Voltage droop

droop = L x di/dt + I x Z_decap

Worked example

With the default values below, Voltage Droop Calculator returns Voltage droop of 1,545.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Load current step: 25 A
Power delivery inductance: 120 pH
Current rise time: 2 ns
Decoupling network impedance: 1.8 mΩ

Results

Voltage droop: 1,545.00 mV
Inductive droop component: 1,500.00 mV
Resistive droop component: 45.00 mV
Droop at 0.85 V supply: 181.765% %

Step by step

1Values used
2Voltage droop
3Voltage droop= 1,545.00 mV
4Inductive droop component= 1,500.00 mV
5Resistive droop component= 45.00 mV
6Droop at 0.85 V supply= 181.765 %

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does inductance dominate fast transients?

Because L di/dt scales inversely with rise time. A nanosecond-scale current step sees inductance that is invisible at DC.

What suppresses first-droop?

On-die capacitance, which has negligible inductance to the load. Package and board capacitors handle progressively slower droop events.