Parts List/Tune Up Info

CC2642R

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SWRS194G –JANUARY 2018 – REVISED APRIL 2020

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Application, Implementation, and Layout

7.2 Junction Temperature Calculation

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 three recommended ways to derive the junction temperature from other measured

temperatures:

1. From package temperature:

(1)

2. From board temperature:

(2)

3. From ambient temperature:

(3)

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 Section 5.8.

Example:

Using Equation 3, the temperature difference between ambient temperature and junction temperature is

calculated. In this example, we assume a simple use case where the radio is transmitting continuously at

0 dBm output power. Let us assume the ambient temperature is 85 °C and the supply voltage is 3 V. To

calculate P, we need to look up the current consumption for Tx at 85 °C in Figure 5-8. From the plot, we

see that the current consumption is 7.8 mA. This means that P is 7.8 mA × 3 V = 23.4 mW.

The junction temperature is then calculated as:

(4)

As can be seen from the example, the junction temperature is 0.6 °C higher than the ambient temperature

when running continuous Tx at 85 °C and, thus, well within the recommended operating conditions.

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, etc. 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 Measuring

CC13xx and CC26xx current consumption.