AN2344

Conclusion

23/27

4

Conclusion

Here are a few reminders:

●

must always be below the absolute maximum ratings in the DUT datasheet.

●

Any high frequency repetitive avalanche may result in device failures, depending on the

actual consistency of the heat sink used.

●

All manufacturers' production testing is performed only for some milliseconds and that

a “pass” is simply defined as a device that has survived without destructive damage.

●

Stresses of highly localized peak temperatures and currents at the “microscopic” levels

on the MOSFET are impossible to identify. All manufacturing processes are intended to

produce uniform and consistent test results (e.g. Rb and Beta). but this does not mean

that any single device amongst these, up to several thousands from a single wafer are

perfect, even if it survives the short production test.

●

The reliance on data sheet avalanche ratings, even if the in-circuit stresses are not

carefully calculated or characterized, is motivated by a potentially significant circuit cost

saving. The apparent respect of the ratings at certain standard “in lab” conditions

cannot be easily and safely generalized to all normal or abnormal events that can

happen in the real world application environment. Accepting and tolerating - at least as

worst case - the use of the avalanche characteristics of the Power MOSFET in

applications where such behavior is not strictly required, must take into account the risk

of a reduced guard-band for withstanding events and any other variations that can be

correlated with the application failure.