There are two ways to calculate the junction temperature Tj: from the ambient temperature Ta or package upper surface center temperature Tt. With an IC power loss Pd, Tj can be calculated as follows:
Tj = Ta+θja × Pd
Tj = Tt+ψjt × Pd
.θja is the thermals resistance between the junction and Ta, ψjt is the thermal resistance between the junction and Tt, and Pd is the power consumption=(Vin-Vo)×Io+Vin×Icc Related Link:Technical Document