Reviewing Gate Branches for Parallel Power MOSFETs

Parallel MOSFETs can share steady current reasonably while carrying unequal current during switching. Gate charge, threshold, parasitic inductance, and branch impedance influence which device turns on first and off last. Review the gate network and physical power paths together before dividing total current by device count.

Draw each device as a separate branch

Show individual gate connections, source returns, drain paths, and any shared resistance or inductance. The Nexperia note on paralleling power MOSFETs discusses dynamic sharing and arrangements with local and common gate resistance. Its recommendations depend on the switching configuration, so avoid applying a universal resistor value to every parallel bank.

Identify whether the driver senses or references a power source path that also carries large current. Shared source voltage changes can affect the effective gate drive differently across the devices.

Compare relevant tolerances

Review gate charge, threshold, on resistance, and their temperature behavior using the selected device data. Nominally identical part numbers do not imply identical switching times. Check whether the application requires additional characterization or selection beyond ordinary production tolerances.

Include driver source and sink capability for the combined gate load. Increasing the number of devices changes both total charge demand and the network’s dynamic behavior. A driver that handled one device may no longer produce the same gate waveform with several attached.

Measure individual behavior

Observe gate to source voltage at each device and compare current sharing with a method that does not substantially disturb one branch. Aggregate current alone cannot identify a device that momentarily carries most of the load.

Check turn on and turn off separately at representative load, voltage, and temperature. Keep probe connections symmetrical where possible and account for their added loading. A measurement wire inserted into one source path can change the very imbalance being investigated.

Evaluate electrical and thermal evidence together

Compare steady temperatures after reaching the intended thermal condition, but do not use temperature as the only indication of switching current. Unequal cooling and copper paths can create temperature differences even when electrical sharing is similar.

Save branch geometry, resistor placement, drive waveforms, individual current evidence, and thermal conditions. Review relevant transients and fault response as well as nominal operation. The acceptance decision should show that every device remains within its reviewed stress limits. It should not rely on a simple arithmetic division of the total current or on the assumption that a positive resistance temperature coefficient automatically solves dynamic sharing.