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TPS62130A-Q1: Calculating the Junction Temperature

Part Number: TPS62130A-Q1
Other Parts Discussed in Thread: TPS62130

We have estimated the power dissipation on the TPS62130A-Q1 mounted on a 10-layer HDI PCB as 0.7W based on measured data.

The thermal resistance parameters mentioned in the datasheet are as below:

In our measurement setup, we are measuring the temperature on the component top and on the PCB right next to the component as shown below:

Q1: Can we calculate the instantaneous Junction Temperature (TJ) based on the formula given on page 8 of this app note ?

Measured Tc (Thermocouple Ttop from the picture) = 116 C

Hence, TJ = 116.6 + 0.7 x 1.1 = 117.37 C

Q2: We worked out the TJ based on Equation 4 in the same document, fully aware of the caveats mentioned in the explanation.

Measured Tc (Thermocouple TC from the picture) = 115.3 C

Hence, TJ = 115.3 + 0.7 x 4.5 = 118.45 C

This number is close to the value obtained using Equation 8, assuming that the point of measurement is really really close to the bottom case of the device.

Are we on the right track here?