Question about LMR14030 thermal resistance : RθJC

Hi 

I just found some questions about thermal resistance RθJC  in LMR14030

According to JEDEC's specification of thermal resistance, RθJA=RθJC+RθCA.

So in this case RθJA should be greater than RθJC

However, in the specification of LMR14030, it is obvious that RθJC is larger than RθJA, which is not in accordance with the thermal resistance standard defined by JEDEC. 

Can you help confirm why the RθJC is larger than RθJA in LMR14030?

Thanks

Jason

Johnsin Tao：

回复 KW X:

Hi看一下下面文档第6~7页：www.ti.com/…/spra953c.pdf

Jason Cheng1：

回复 Johnsin Tao:

Hi 

感謝回覆

我有詳細讀過這份文檔

裡面對θJA的定義為"Junction-to-Ambient的熱阻", 也就是當所有熱量從晶片結到周遭環境的熱阻

θJC的定義為"Junction-to-Case的熱阻", 也就是當所有熱量都從晶片結到封裝頂部表面的熱阻

以定義來看應該要θJA>θJC, 因為θJA=θJC+θCA, θJC比起θJA還少了θCA的熱阻值(如下圖)

目前我看了許多資料也沒看到有θJC>θJA的說明

所以想知道LMR14030為什麼θJC>θJA?

Thanks

Jason