This application note introduces Fairchild's single-pulse unclamped inductive switching (UIS) rating curves. These curves are used to evaluate the power MOSFET's tolerance to transient voltage surges under single-pulse UIS conditions. These curves can help designers select the most suitable MOSFET for their application when designing applications.
The document describes failure mechanisms in power MOSFETs, distinguishing between early devices that failed due to parasitic bipolar turn-on and modern rugged devices like the Fairchild PowerTrench line which fail via thermal limits. It introduces a specific rating curve for single-pulse UIS events based on starting junction temperature.
| Starting junction temperatures for rating curves | 25°C and 150°C |
|---|---|
| Effective avalanche voltage factor | 1.3 times rated breakdown voltage |
The effective avalanche voltage (Vosxisus) is approximately 1.3 times the rated low-current breakdown voltage (BVpss).
The failure current versus the time in avalanche closely approximates a negative one-half slope when plotted on a log-log graph.