Hello team,
We can find Rja=80.3C/W on the datasheet in TPS745.
I believe that Rja in most of the TI devices should be measured based on JEDEC High-K, but I also found that the Rja is not same as JEDEC High-K from the application report in the link below.
It describes that the 80.3C/W is different from JEDEC High-K of 61.3C/W. (Please take a look at Figure 7 in the report.)
Is there any reason why they are distinguished to be defined?
Thanks in advance.
S.Sawamoto
Hi Sawamoto-san,
The application note that you are referring to created different PCBs which were used to calculate the actual Rja on the real boards so we could evaluate the effect of various layouts. One of those layouts was an approximation of the JEDEC High-K board, however the real JEDEC High-K board is not a functional layout as there are not components on the board and the device is not routed properly (instead all traces on the pins go straight to the edges of the board. This is why there is a difference between thermal metric listed in the datasheet and the value measured on the approximation board.
Below is a copy of a slide used to describe the JEDEC High-K standard and then a picture of the approximation board for comparison sake.
