Evaluating of the Avalanche Failure of Power MOSFETs using Atlas
Introduction
Power MOSFETs are widely used with an inductive load for S/W power supplies, DC-DC converters, and so on. But due to high frequency operation, the surge voltage applied to the MOSFETs at turn-off depends on the inductance and parasitic inductance in the circuit. For some operation modes, the pulse width for the turn-on or off will be very short, and the device fails due to the short surge period.
In this article, the device simulator ATLAS was used to to predict the maximum inductive loads and find out the failure current due to the device intrinsic temperature.
Single Pulse Unclamped Inductive Switching
Figure 1 shows that the single pulse unclamped inductive switching (UIS) test circuit for avalanche testing. Figure 2 shows the traditional operation waveform (avalanche operation waveform)[1].
The avalance current (IAV) depends on both the inductance value and the direction of the on time (PW). Therefore, to get a high IAV a small inductance or a long on time should be chosen.
From the circuit shown in Figure 1, the single pulse avalanche energy (EAV) can be calculated:
