Junction temperature of the chip (T_j) can be calculated using either of the two equations shown, depending on whether θJA (Theta J-A) or ΨJT (Psi J-T) is used. Whichever equation is used, the power consumption (P) is essentially the product of the power supply voltage and the power supply current for the IC. Keep in mind the IC functions (whether it is a power supply IC or an op-amp), the output load current, and other factors must also be considered. In all cases, however, the power consumption is determined from the current and voltage consumed by the IC. Ensure that the calculated T_j is less than the specific T_jmax in the datasheet. If calculated Tj is higher than T_jmax, then modifications in the operating point of the part or the PCB design need to be done.