2.2 Thermal Equations

The generic equation to compute T_J is the following:

T_J = T_A + R_J-A x P_TOT

where:

• T_J is the junction temperature,
• T_A is the ambient air temperature,
• R_J-A is the junction-to-air thermal resistance (see Junction-to-Air Thermal Resistance for details),
• P_TOT is the total power consumed in the product.

The device data sheet limit on T_J (T_{J_Limit}) induces a limit on T_A, as shown in the following equation:

T_{A_MAX} = T_{J_Limit} - R_J-A x P_TOT

The maximum ambient temperature (T_{A_MAX}) an application can support is a function of T_{J_Limit}, the total power dissipation and the junction-to-air thermal resistance.