Understanding Power MOSFET Avalanche Operation
The power function of a MOSFET operating in avalanche can be of any form. This application note covers a specific avalanche power function that forms the basis of avalanche ratings found on power MOSFET data sheets. MOSFET data sheets typically specify avalanche ratings under the synonymous terms "UIS" or "UIL" meaning "Unclamped Inductive Switch-off" or "Unclamped Inductive Load".
That is, power MOSFET avalanche ratings apply to the resultant Vds and Is for p-channel MOSFET) waveforms when a MOSFET driving an unclamped load is switched off.