Analysis and modeling of DMOS FBSOA limited by n-p-n leakage diffusion current

Abstract

Failure of DMOS self-heated in saturation below the avalanche threshold is usually related to an activation of the parasitic n-p-n transistor. In this work we show that the exponential increase of the leakage diffusion current of the n-p-n is sufficient to cause thermal runaway, even for a slightly reverse body-source bias caused by the internal ballasting source resistance. Adding this current contribution to a basic DMOS compact model allows simulating the thermal limit of large DMOS transistors considered as distributed electrothermal networks. To our knowledge it is the first report of a quantitative DMOS FBSOA model accounting for the instabilities driven by the temperature dependences of both MOS and n-p-n components