TPS7A8300: Thermal performance for the two available packages

Cosmin,
The thermals are correct. The primary path of heat flow is immediately below the die, so, additional package area that is not below the die only marginally improves the thermals.
Regards,
Mike

Understood, but the numbers are worse for bigger pad Rojc(bott): that is 1.6C/W for the big pad and 1.0C/W for the small pad which is opposite to improved thermals... what am I missing?

Cosmin,
I believe that is due to the way that the measurement is performed. The source of the heat is the die, and the Rjc is measured from the die to the edge of the package. Since the edge of the package is actually closer to the source of the heat in the RGR package, the Rjc is lower.
Regards,
Mike

Hello Mike,

I think that you are referring to Rtheta-junction-to-board which is measured with the thermal probe placed sideways.

I am referring to Rtheta-junction-to-case-bottom which is measured right underneath the thermal pad - this is where it does not make sense: the bigger pad (same die) has higher thermal resistance, 1.6C/W for the big pad RGW and 1C/W for the small one RGR...

Thank you

Hi Cosmin,

The following Application Report goes into some detail on how the different thermal metrics are measured:
www.ti.com/.../spra953c.pdf

Very Respectfully,
Ryan