Semiconductors
Model class: Exact ideal relationship
MOSFET parallel-current sharing
Estimate static current sharing between two parallel MOSFETs from their on-resistance values.
Interactive engine
Start with the stated conditions.
Values stay in this browser. Choose a representative scenario, then calculate deliberately.
Example ready
Calculate to inspect the result.
The result will identify the direct answer, assumptions, and any warning that changes the next decision.
Assumptions to check
- The entered MOSFET-current-sharing values represent the stated operating condition.
- This exact ideal relationship is evaluated in the declared lumped or first-pass model.
- A MOSFET-current-sharing calculation is not a component qualification or safety approval.
What this MOSFET-current-sharing calculation establishes
Estimate static current sharing between two parallel MOSFETs from their on-resistance values. The useful result is the stated electrical quantity and the decision it supports, not an unstated claim about a finished product. This engine keeps the governing relationship visible so an input, unit, condition, or model boundary can be reviewed before a value becomes a component or layout choice.
Each branch current follows an ideal resistive current divider using the two entered on-resistance values. Treat the number as a first-pass result for the declared operating point. When a source, load, temperature, frequency, waveform, component tolerance, or measurement condition changes, repeat the calculation at the relevant corner rather than assuming the nominal answer persists.
Worked decision context
Two branches of 10 mΩ and 12 mΩ carrying 22 A total share 12 A and 10 A respectively in the isothermal resistive model. That example verifies the equation and illustrates the scale of the result, but it does not select a part by itself. Compare the result with available values, ratings, tolerance bands, and the receiving circuit or physical environment before implementation.
Use the primary output to identify the binding constraint. If it leaves little margin, document which input dominates and use selected-part data, a higher-fidelity model, simulation, or measurement. This is especially important when a small numerical difference changes a thermal, timing, noise, or reliability decision.
Limits and validation handoff
Real Rds(on) rises with temperature; without thermal coupling the hotter, higher-current device can run away. Verify with the stated thermal-coupling model. The calculation does not silently include omitted parasitics, installation conditions, manufacturing variation, or product policy. Those conditions can be decisive even when the arithmetic is exact for the selected model.
Record inputs, units, model assumptions, and the intended decision with the result. Verify the leading risk against the selected component data sheet and a representative measurement when the circuit has consequential energy, high voltage, safety, compliance, or reliability requirements.
Common mistakes
- Treating the MOSFET-current-sharing result as a guaranteed operating limit rather than a first-pass exact ideal relationship estimate.
- Mixing a data-sheet value measured under one condition with this MOSFET-current-sharing calculation performed at another.
- Selecting a component before checking the boundary this calculation names: real Rds(on) rises with temperature; without thermal coupling the hotter, higher-current device can run away. Verify with the stated thermal-coupling model.
Model limit and handoff
Keep the entered MOSFET-current-sharing conditions with the calculation, then validate the binding limit using the selected component, physical implementation, and representative operating corner.
FAQs
Is this MOSFET-current-sharing result sufficient to approve a design?
No. It applies exact ideal relationship reasoning to the entered MOSFET-current-sharing values and names the checks that still need selected-part data, a higher-fidelity model, or measurement. Real Rds(on) rises with temperature; without thermal coupling the hotter, higher-current device can run away. Verify with the stated thermal-coupling model.
What does this MOSFET-current-sharing calculator assume that could make the result wrong?
Each branch current follows an ideal resistive current divider using the two entered on-resistance values. If the entered values do not match the real operating condition, the result no longer describes the actual circuit.
Where should this MOSFET-current-sharing result go next?
Compare this MOSFET-current-sharing result with MOSFET datasheets and SOA, then use the stated next decision below the calculator to move from this first-pass number toward an implementation.