December 2013

DocID025511 Rev 1

1/10

TN1156

Technical note

Irradiated HV Power MOSFETs working in linear zone: a

comparison of electro-thermal behavior with standard HV products

Introduction

This paper studies the thermal instability phenomenon of irradiated HV Power MOSFET

devices working in linear zone operating conditions and compares their electro-thermal

behavior with standard products. Experimental results show that irradiated devices have

more thermal instability than standard devices, therefore, they should be used carefully in

these particular operating conditions.

In most of cases, Power MOSFETs are used in switching operating conditions where

R

DS(on)

is the key parameter to evaluate the device’s performance. However, in some

special cases, devices work in linear zone. A Power MOSFET works in linear zone when

high-currents and high voltages are together applied to MOSFET terminals. Power

MOSFETs are used in linear zone in some dedicated applications especially in automotive

segment such as: standard topologies of audio amplifiers, linear DC-DC converters, DC fan

controllers, electronic loads, current mirrors, smart fuses, etc… In many of these

applications, typically, the LV Power MOSFETs are used. Furthermore, Power MOSFETs

work in linear zone for a short period of time when they are used in switching conditions

during the Miller region where high-currents and high voltages are together applied to

MOSFET terminals. This means that the thermal instability must be also evaluated in

applications where linear zone isn't the typical operating condition. Therefore, this

phenomenon needs to be evaluated even during the slow switching process either in LV or,

in particular, in HV Power MOSFETs when high inductive loads are driven. Considering a

theoretical Power MOSFET FBSOA, linear zone is referred to that area delimited by

maximum allowed dissipated power for different power pulse duration.

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