Gate Charge and Driver Supply Current: Average Demand Differs from Transition Current

Name the current being calculated

TI distinguishes average gate-drive demand and gives Qg times switch count times switching frequency for its corresponding model. Primary reference: average gate-drive current, section 1.5.2.

Average supply demand is not the same quantity as a driver’s peak source or sink capability. The charge conditions and the number of switching devices must remain explicit. A transition also has a changing waveform, so one average does not describe every instant.

An invented charge budget

Assume a fictional applicable gate charge of 30 nC, one device and 20 kHz repetition. The modeled average gate-charge supply current is 30 nC×20,000/s =0.60 mA. If the same 30 nC is transferred in 100 ns in a separate idealized transition comparison, Q/Δt is 0.30 A over that interval.

Those results differ by orders of magnitude because their averaging windows differ. The transition estimate does not establish a real gate waveform or prove a selected driver adequate. It simply prevents average supply current from being substituted for transition-current capability.

Keep the two review questions separate

Prepare separate columns for charge condition, switch count, repetition rate, average supply contribution and the intended transition evidence. Add quiescent and other supply contributions to their own terms.

Ask how the real gate path and waveform support the required switching behavior. This worksheet clarifies both a supply-current budget and a driver comparison while leaving component selection to the applicable circuit assessment.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• Primary reference: average gate-drive current, section 1.5.2