Decoupling Capacitance Requirement Calculator
Work out decoupling capacitance requirement instantly with clear inputs, formula shown and shareable results.
About Decoupling Capacitance Requirement Calculator
Decoupling capacitance must supply the charge the load demands before the regulator responds: C = I x t / allowed droop. ESR eats into that droop budget directly, so a high-ESR bulk capacitor can make the requirement impossible however large its capacitance.
Formula
Decoupling
C = delta_I x t_response / delta_V_allowed; ESR contributes I x ESR of droop immediately
Worked example
With the default values below, Decoupling Capacitance Requirement Calculator returns Capacitance required of 3,000.00. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Current step
- 18 A
- Allowed droop
- 30 mV
- Time until the regulator responds
- 500 ns
- Capacitor ESR
- 1.5 mΩ
Results
- Capacitance required
- 3,000.00 µF
- Charge to supply
- 9.00 µC
- Droop from ESR alone
- 27.00 mV
- 100 nF capacitors equivalent
- 30,001 capacitors
Step by step
- 1Values used
- 2Decoupling
- 3Capacitance required= 3,000.00 µF
- 4Charge to supply= 9.00 µC
- 5Droop from ESR alone= 27.00 mV
- 6100 nF capacitors equivalent= 30,001 capacitors
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, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 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 ESR matter more than capacitance sometimes?
Because the ESR drop appears instantly and cannot be reduced by adding capacitance in the same part. Paralleling capacitors reduces effective ESR, which is why many small ones beat one large one.
What sets the response time?
The voltage regulator's control loop bandwidth. A 1 MHz loop needs decoupling to cover roughly a microsecond of transient on its own.
Related Calculators
You might also need
- Block RAM Requirement CalculatorAlso in Semiconductor, VLSI & Hardware Design
- DSP Slice Requirement CalculatorAlso in Semiconductor, VLSI & Hardware Design
- Amdahl Speedup CalculatorAlso in Semiconductor, VLSI & Hardware Design
- ATE Throughput CalculatorAlso in Semiconductor, VLSI & Hardware Design
- Bitstream Size CalculatorAlso in Semiconductor, VLSI & Hardware Design
- Burn In Time CalculatorAlso in Semiconductor, VLSI & Hardware Design