We would like to use this MPM3833C. As per the calculation 1.42W power will dissipate according to our load. Our ambient temperature is 70 degree Celsius. what could be the maximum junction temperature?. As per the thermal simulation it is reaching up to 162 Degree Celsius. We used the network analysis model considered these following values TJa = 50 C/W TJc = 12
It looks to me like you goofed on the calculation a little bit. I get 1.42W times 50C/W junction to ambient gives a 71 degree rise of the junction above the 70C ambient for a junction temp of 141.
It looks to me like you used a junction to case + junction to ambient resistances in your calculation which would double count the junction to case component.
You can do a lot with thermal vias, to lower the thermal resistance
can you have any reference document? which can explain the case temperature with respect to load?