You are missing the point of what AMD is declaring with their TDP number
They are not telling that power is same thing with temperature.
Nowhere near that. This is applied physics (thermodynamics).
They are telling to the cooler manufacturers that under a specific tCase (CPU IHS surface -lid- temp), a specific tAmbient (ambient air temp on inlet of the cooler's fan) and a specific thermal resistance cooler (HSF θca) an X amount of heat will be transferred from the IHS to the ambient air.
So cooler manufacturers have to design coolers that comply (to a minimum) to those parameters.
In order to understand this you have to understand first how heat transfer works. Roughly It involves a temperature (t)Delta between 2 objects/surfaces and the thermal resistance of what is in between them.
The higher the tDelta as the temp difference between 2 objects and the lower the heat resistance between them the more heat will be transferred and vise versa.
As tDelta they are meaning the CPU IHS surface temp (tCase) and the air temp on the inlet of the cooler fan (tAmbient).
Thermal resistance of cooler is HSF (HeatSink-Fan) θca (theta c a, measured in °C/W)
(tCase - tAmbient) / (HSF θca) = TDP
In their formula they are taking as granted the tAmbient will be 42C (as an inside of a case that has been wormed up by the system)
View attachment 263747
So cooler manufactures on minimum they have to come up with a HSF design that can maintain the CPU IHS surface at 61.8C under 42C ambient, when the CPU is on maximum power draw. In case of 3900X is the 142W (PPT).
So... if they slap on top of the 3900X a HSF with thermal resistance at least of 0.189 °C/W the transferred heat will be ~105W.
Reasonable question:
But the CPU is "producing" 142W of heat as all the electrical energy is transformed into thermal energy... Where is the heat between 105W and 142W?
This is not mentioned anywhere but you have to think that this system (CPU, HSF, ambient) is not a closed/sealed one from the rest of the world.
The CPU is in contact with the board through the socket and also some air is around the outer edges of the CPU.
So the rest of the heat 142-105= 37W will be dissipated by the board from the surrounding components and the back of it. Yes boards are hot around the socket of a 142W CPU on max power.
And this should be true on those parameters (tCase/tAmbient/θca) AMD specifies.
Here is AMDs claims of TDP:
"TDP is about thermal watts, not electrical watts. These are not the same.
TDP is the final product in a formula that specifies to cooler vendors what thermal resistance is acceptable for a cooler to enable the manufacturer-specified performance of a CPU.
Thermal resistance for heatsinks is rated in a unit called θca ("Theta C A"), which represents degrees Celsius per watt.
Specifically, θca represents thermal resistance between the CPU heatspreader and the ambient environment.
The lower the θca, the better the cooler is.
The θca rating is an operand in an equation that also includes optimal CPU temp and optimal case ambient temp at the "inlet" to the heatsink. That formula establishes the TDP.
linuxreviews.org
I cannot break it down better than this, I'm sorry.