For the automotive version ADV7391WBCPZ the temperature range is specified for −40°C to +105°C. I assume this is ambient temperature?

Please confirm.

But the important value to make sure the part does not violate the spec is the Tjunction from the ABSOLUTE MAXIMUM RATINGS, which is speced up to 150°C, correct?

The datasheet gives 2 different thermal resistance values for junction to case (θJCtop and θJCbottom). How have both values to be combined to calculate the temperature at a given power consumption level?

best regards

Joerg

Hi Joerg,

There is no "has to be", there is no definitive answer or formula that settles the question. Treating them in parallel is one way to deal with it. I've seen it done using approximation from a resistor network from the junction to ground on either side with thermal resistance substitued for electrical resistance and voltage for temperature-- heat flow becomes current. This would give you a general idea of the boundary conditions.

There are a lot of ways to do these approximations but they all have their drawbacks-- that's why that data sheet has no formula.

Generally, if there is a Theta JCbottom (or Theta JB), then there is a ground slug and that path sinks most of the heat and so another approach is to simply ignore the top and use the basic formula.

The actual accurate number is heavily influenced by the system characteristics anyway so if you are considering the chip in isolation then you are really only going to get some rough boundary conditions anyway.

Dave