Let me check this is right..
8A x 14V is 112W
112W x 0.45 deg C/W Junction to Case is 50.4 deg C.
50.4 deg C + 30 deg expected ambient is 80.4 deg.
80.4 deg C is less than the datasheet Operating Junction Max Temp of 170 deg C.
It's Junction to Ambient is 62 deg C/W.
No heatsink needed - or have I got it completely backwards?
If it was dissipating 112W without a heatsink then the temperature to ambient would
be 62 * 112 = 6.7kW !! But of course its not dissipating 112W.
You have to add the thermal resistances together, and if there is no heatsink you have
to add the 62 C/W (otherwise you add the heatsink's thermal resistance to ambient).
The 0.45 C/W is really only relevant if you bolt the device onto a water-cooled mass of
During switching the MOSFET might briefly be carrying about 4A at 7V (assuming
a resistive load) when the channel resistance matches the load resistance, and this is
the maximum dissipation during switching (28W or 25% of the full load). However this
might only be for 1us, so its only an issue when the switching is at a high frequency
so that the proportion of time spent switching is non-negligible.