Junction temperature of CoolSET™ should be within the operating range to have a reliable power supply. As junction is not accessible, CoolSET™ thermal characterization parameters RthJA and ΨJT are determined to obtain the junction temperature of the device.
The junction temperature TJ1 of the CoolSET™ can be calculated using below equation (Eq. 1) using RthJA in the datasheet.
where:
PD – power dissipation of the CoolSET™
TA – ambient temperature
In actual application, the test conditions used in RthJA thermal characterization is usually different from the actual setup and the calculated TJ may not be as accurate due to different PCB copper area, surrounding components, airflow etc. Therefore, a better alternative is to use junction to top-center thermal characterization parameter ΨJT instead to calculate junction temperature TJ2 given in below equation (Eq. 2).
where:
TTS – CoolSET™ top surface case temperature
The use of ΨJT should not be confused with RthJC which is the thermal resistance from the device junction to the external surface of the package held at a constant temperature.
RthJA is defined in the datasheet. For ΨJT value, contact technical support.