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10.2 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:

TJ = ψJT × P + Tcase

(1)

2. From board temperature:

TJ = ψJB × P + Tboard

(2)

3. From ambient temperature:

TJ = RθJA × P + TA

(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 Thermal Resistance Characteristics.

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

10 dBm output power. Let us assume the ambient temperature is 85 °C and the supply voltage is 3.6 V. To

calculate P, we need to look up the current consumption for Tx at 85 °C in Section 8.22. From the plot, we see

that the current consumption is 14.4 mA. This means that P is 14.4 mA × 3.6 V = 51.8 mW.

The junction temperature is then calculated as:

TJ = 23.4

° C

× 51.8 m W + TA = 1.2 ° C + TA

(4)

As can be seen from the example, the junction temperature is 1.2 °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.

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CC1312R

SWRS210H – JANUARY 2018 – REVISED NOVEMBER 2020

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CC1350 Datasheet(PDF) 65 Page - Texas Instruments