I'm building a device containing a large number of ICs. Now, I'm 99% certain heat won't be an issue. (Considering the volts and amps involved, I doubt you could accurately detect the amount of heat involved.) But, just for argument's sake, how would you go about calculating this stuff?
My first thought was to look at the datasheet. But it doesn't seem to say anywhere "this chip will produce X units of heat in normal operation". (Presumably because there's too many different variables that affect it, so they can't easily come up with a definitive number.)
The only relevant thing I can see is a section on "thermal resistence". If I'm understanding this currently, this is a measure of how quickly any heat generated would be able to escape the casing. (Presumably depending on how hot inside vs how hot outside; it seems to be expressed in units of °C/W.)
Clearly thermal resistence is part of the equation. But without knowing how much heat per second the IC produces in the first place, I'm not sure where to start with this.
Best Answer
Here is rather simplified answer: with few exceptions (like light emitting or RF radiating) the electronic circuits convert all incoming power into heat. So, if you measure the power consumed by your assembled device you can get pretty good approximation of the heat to be dissipated.
Of course, if you want to calculate it in advance or predict temperature in various conditions you need all those things described in @SpehroPefhany's answer.