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LM5116: Unstable efficiency behaviour

Fons van Heese1
Prodigy 10 points
Part Number: LM5116

Tool/software:

We use the LM5116 in a 24V to 12V configuration. Outputcurrent is typical 0.8A. Maximum output current is about 2 .. 3 A. Frequency is 250 kHz. 
We use Vishay coil IHLP-4040EZ-11 22uH.
We produced al lot of PCBA's without problems (>200)
Now we have some boards where the input current is double, coil becomes that hot the soldering is almost melting.
The phenomena follows the coil, if we mount it on a different board, we see the same high current effect.
If we replace the coil with a other identical part, problem solved.

Anybody with similar experiences and recommendations to solve this?

  • 0
    TI__Guru 58851 points

    Hello Fons

    Looks like the issue is caused by the inductor itself since the problem solved by replacing the inductor. Please check if any insulation issue in the inductor. And please check the soldering quality by using IR camera. A cold solder joint results in high resistance at the joint, and then the high resistance can cause an excessive heating.

    -EL

  • 0 in reply to EricLee
    Prodigy 10 points

    Finally we checked the 2 failed inductors by measuring inductance of these 2 parts. Done by measuring time constant and comparing them with good working inductors. The 2 failed inductors have an 10 times lower inductance, most likely about 2u instead of 22u. Next question: How can this happen, during PCBA production, testing, transport, assembling in machine?

  • 0 in reply to Fons van Heese1
    TI__Guru 58851 points

    Hello Fons 

    You may have to contact the inductor manufacturer to get the answer. If no insulation issue, it might happen in their production line.  

    -EL