TPS73733DCQR

Hi Maheswari,

While we have a lot of articles on LDO's and thermals, I agree we are missing the very simple answer.

The way I often describe it is that you use Theta JA for estimating the thermal performance, and Theta JC for confirming the thermal performance.

So that being said, Theta JA is the Degree's C per Watt rise above the Ambient and the number given is for a Jedec standard High-K board. For LDO's it is best to use the PCB ambient and not room temp. If your application is from 2.5 to 1.8V at a maximum current of 1A, then your power dissipation is 0.7W and the estimated junction rise above ambient would be 0.7W*TJA. The TJA does vary based on package and typically the smaller the better.

Once you have a PCB in hand, TJC can help confirm the actual die junction temperature in the application. This is done by adding a thermo-couple to the top of the die and measuring the temperature. Here you add the TJC*0.7W to the temperature measured to estimate how hot the die really is.

I find in practice it is very hear to use TJB as it is close to impossible to get a thermo-couple between the device and the PCB.

For a more detailed description you may want to look at the following www.ti.com/.../slua844a.pdf

I hope this helps to clarify the difference between these parameters.

If not, please do not hesitate to ask again.