Based on the input/output voltage, input current and the efficiency we estimate the part dissipates a total of 2.24W. Under this condition we measure the case temperature by attaching a thermal couple on the case (top) and it reads 64 C. The device has a thermal pad. Eight thru hole vias are placed on the circuit board beneath the thermal pad. The circuit board is in open air without air flow. The ambient temperature is about 25C. Given these conditions how should we estimate the junction temperature? The datasheet lists the following thermal information, which piece(s) should we use and why?
RθJA Junction-to-ambient thermal resistance 29.8 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 14.9 °C/W
RθJB Junction-to-board thermal resistance 6.3 °C/W
ψJT Junction-to-top characterization parameter 0.2 °C/W
ψJB Junction-to-board characterization parameter 6.3 °C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance 0.8 °C/W
Thanks
Nikko
