LTM4653 - optimal thermal PCB layout and thermal theda values

Question

Hello, 
 1) What is the optimal thermal PCB layout? Does the evaluation board DC2327A represent the optimal thermal PCB layout? 
 2) The datasheet has several thermal theda values: theda_JCtop = 20.6, theda_JCbottom = 5.1, theda_JB = 6.0, theda_JA = 15.5. Which would I use for analysis of the BGA packaged soldered to the board without a heatsink? I am particularly confused about the difference between theda_JCBottom and theda_JB. I want to take advantage of the theda_JCbottom thermal resistance, but I am unsure what PCB layout and assembly configuration resulted in theda_JCbottom. 
 Thank you!

Fil · Answer

The evaluation board is a good starting point. It is optimized including EMI and thermals performance. Thermal testing on your actual board design is recommended.

dkb · Answer

Hi 
 1) DC2327 represents a good design. 
 2) I was able to dig up the archives on this model and found that it was in fact simulated on a detailed and optimized pcb. It appears the JCbot value of 5.1 is a good one. Also, the difference between the JCbot and JB is that the pcb is sinked for JCbot and not sinked for JB. 
 Regards

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LTM4653 - optimal thermal PCB layout and thermal theda values

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