What is the maximum junction temperature and junction-to-ambient thermal resistance of NS9215 microprocessor?

The only data we received from the FAB is in ns9215 HRM:

Junction temperature TJ 125°C
Theta Ja = 31.7 oC/W
Tj = Ta + (Theta Ja x W)
Tj = Temperature junction
Ta = Temperature ambient
Theta Ja = Junction to ambient
W = Power in Watts

Junction-to-ambient thermal resistance is a measure of the ability of a device to dissipate heat from the surface of the die to ambient via all paths.
 Psi-jt = 2.5 oC/W
Tj = Tc + (psi x W)
Tj = Temperature junction
Tc = Case Temperature
Psi = Thermal coefficient tying the case to the junction
W = Power in Watts

Psi-jt is measured at the top of the package in the center. Under natural convection, psi-jt for a plastic package is generally a relatively low value.
This means that Tj is usually just a little hotter than the top of the package. The die is physically separated from the top surface by only a thin region of plastic mold compound. So unless the top is forcibly cooled by significant airflow there will be very little delta-T between them.
Last updated: Jun 28, 2019

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