LM3404 Case Temperature

Perhaps you can find your info here: http://www.ti.com/lit/an/snva238/snva238.pdf 

Excellent App Note. Thanks.

The only thing is dont understand is where the switching loss equation comes from:

PS = 0.5 x VIN x IF x (tR + tF) x fSW

If you can point that out it would be very helpful. Why is it not a similar type of equation to

PC = (IF x D)2 x RDSON  ???

The losses on a switching system are mainly during conmutation, not on high or low status. When going from switch closed to switch open, the voltage over the switch goes up from 0 to Vin. The current, on the other side, goes from If to zero. The situation where the switch goes from open to closes is similar.

You can also simulate the system in Webench at www.ti.com :-) There you often can see the IC temperature at given specs and conditions (temperature and PCB size and so on).