Quote:
Originally Posted by
Geonerd 
What causes the driver to overload? Perhaps the FETs response time or input capacitance starts to increase as it heats up and/or ages? None of the product datasheets I've seen mention this, but it seems possible. (?)
Excess of temperature, most likely. As a small temperature increase makes a cascade effect.
The MOSFET becomes a bit too hot, the driver section starts to decrease output power to compensate for this excessive temperature (due to thermal protection of the own package), leading to an improperly driven MOSFET, which in turn heats up even more, heating up even more the driver, which literally fails to reach the logic level of the FET gate.
Then the FET stays in a half-on or half-off state, generating horrible amounts of heat due to not being fully on or off, heating the whole package until it blows up.
That's the main issue with DrMOS packages. Also, if one of the MOSFETs shuts down entirely due to excessive heat, the remaining ones risk becoming overloaded, and if the thermal shutdown isn't designed for the whole MOSFET array, there's a very high chance of the remaining powered array exploding due to overheat/overcurrent.
Also note that the resistance of the entire assembly is higher when temperatures rise.
