LM34936: I designed LM34936 similar to EVM board but I issue inductor is getting hot.

Amir Eshraghi

Part Number: LM34936

I have designed board with LM34936 similar to EVM board, which I have an issue that the inductor and R5 is getting hot when I am trying to pull around 4Amp 12V (60C)

Can you tell me what can do this? (I know in an increase of DCR can increase the heat on inductor but why R5). Below is my schematic (PDF) and pcb Layout file.

Please let me know if you have any questions.

Thank you

LM34936.pdf

over 3 years ago

0 Brigitte over 3 years ago

TI__Guru 58225 points

Hello Amir,

The inductor temperature is as well dependent on the AC resistance which is often causing higher temperature rise than the DC resistance of the inductor, At maximum load the inductor will have some increase in temperature due to this.

The resistor needs to handle the full current and therefore the connection to some metal plate is important. In addition, the inductance can cause some issues.

Are you using thermals?

0 Amir Eshraghi over 3 years ago in reply to Brigitte

Expert 1230 points

Thanks for the quick replay, not I am using any thermals, as you can see on the below image. I have used the same BOM as the original EVM board for test purposes, but R5, D1, L1 temp is very high.

In this condition, input voltage is 24V and output is set to 12V and 4Amp

Thank you

0 Brigitte over 3 years ago in reply to Amir Eshraghi

TI__Guru 58225 points

Hello Amir,

On the EVM all these components are cool. The inductor might reach 30C, but not more. So something in your design is significantly different to the EVM. Would you please check the output voltage with an oscilloscope? I wonder if your board is instable.

Please check as well the inductor current.

0 Amir Eshraghi over 3 years ago in reply to Brigitte

Expert 1230 points

I build a new board which temp is much better around 40C on inductor when running 12Voutput 4A output, below is the output when is on the load

Please let me know you have any questions.

Thank you

0 Amir Eshraghi over 3 years ago in reply to Brigitte

Expert 1230 points

Do you have any update on this

Thank you

0 Brigitte over 3 years ago in reply to Amir Eshraghi

TI__Guru 58225 points

Hello Amir,

I think you solved the issue when you built the second board, so no update from my side.

0 Amir Eshraghi over 3 years ago in reply to Brigitte

Expert 1230 points

But I thought temp should not exceed 30c when ambient temp is 25, but mine go all the way to 40c

Thank you

0 Brigitte over 3 years ago in reply to Amir Eshraghi

TI__Guru 58225 points

Hello Amir,

This is dependent on the layout, the used components as well as the copper thickness and layer count. It seems that you are using only 2 layers compared to the EVM, so it is within my expectation that the temperature of the external components is somewhat higher than on the EVM.

In addition the amount of copper you are using and the amount of vias to the other side of the board and the amount of copper there is influencing the temperature.

Please have a look at the EVM layout to see the differences to your layout.

Power management

Power management forum

LM34936: I designed LM34936 similar to EVM board but I issue inductor is getting hot.