To provide reliable operation, worst-case junction temperature must not exceed 125°C. This restriction limits the power dissipation the regulator can handle in any given application. To make sure the junction temperature is within acceptable limits, calculate the maximum allowable dissipation, P_D(max), and the actual dissipation, P_D, which must be less than or equal to P_D(max).

The maximum-power-dissipation limit is determined using Equation 11.

Equation 11.

where:

• T_Jmax is the maximum allowable junction temperature
• R_θJA is the thermal resistance junction-to-ambient for the package (see the Thermal Information table)
• T_A is the ambient temperature

The regulator power dissipation is calculated using Equation 12.

Equation 12.

For wider input range requirement, see the TPS715A.