This section shows the different techniques for calculating the junction temperature under various operating conditions. For more details, see Semiconductor and IC Package Thermal Metrics.

There are two recommended ways to derive the junction temperature from other measured temperatures:

1. From package temperature:
   Equation 1. $T_J={\psi }_{\mathrm{JT}}\times P+T_{\mathrm{case}}$
2. From board temperature:
   Equation 2. $T_J={\psi }_{\mathrm{JB}}\times P+T_{\mathrm{board}}$

P is the power dissipated from the device and can be calculated by multiplying current consumption with supply voltage. Thermal resistance coefficients are found in Thermal Resistance Characteristics.

Example:

In this example, we assume a simple use case where the radio is transmitting continuously at 0dBm output power. Let us assume we want to maintain a junction temperature equal or less than 85°C and the supply voltage is 3V. Using Equation 1, the temperature difference between the top of the case and junction temperature is calculated. To calculate P, look up the current consumption for Tx at 85°C. At 85°C the current consumption is approximately 5.5mA. This means that P is 5.5mA × 3V = 16.5mW.

The maximum case temperature to maintain and junction temperature of 85°C is then calculated as:

For various application use cases, current consumption for other modules may have to be added to calculate the appropriate power dissipation. For example, the MCU may be running simultaneously as the radio, peripheral modules may be enabled, and so on. Typically, the easiest way to find the peak current consumption, and thus the peak power dissipation in the device, is to measure as described in the Measuring CC13xx and CC26xx Current Consumption application report.