Thermal resistance in LDO

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engr_joni_ee

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I have found in a LDO voltage regulator the following information.

Junction-to-ambient thermal resistance = 28 degC

Junction-to-case (top) thermal resistance = 43 degC

This look like strange to me. How the junction-to-ambient is lower then the junction-to-case (top) thermal resistance ?

 

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The thermal vias, lowest Rth, on leadframe, closest to bottom of case....

Top of case is a sandwich, plastic covering die, so much higher Rth ?


Regards, Dana.
 

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Is it not like that, junction to ambient thermal resistance is the sum of junction to case thermal resistance and case to ambient thermal resistances ?

If thermal resistance junction t ambient is smaller compared to thermal resistance junction to case then which way the heat is going faster to the ambient, side ways and not through the top case ?
 

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