The Transition Behavior of Power LDNMOS at the ON-OFF Transient During Unclamped Inductive-Switching (UIS) Test

Although the unclamped inductive-switching (UIS) test is commonly used to estimate the ruggedness capability of a power transistor, the transition behavior of the transistor at the ON-OFF transient state is never discussed until now. From the fundamental physics, the inductor current cannot be changed instantaneously. In this article, how the transistor provides the current to keep the inductor current flowing at the transition state of the UIS test in which the gate voltage is pulled down and the drain voltage still does not rise to the breakdown voltage is investigated. From the measurement and T-CAD simulation, it shows that the inductor current can keep constant at the ON-OFF transient of power transistor during the UIS test which can be attributed to the channel current due to ground bounce, displacement current at the rising time, and electrons/holes leaving the depletion region when the depletion width increases with drain voltage at the rising time.