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LM5155: Need help in operation of boost converter PCB

Faiz Majeed
Prodigy 115 points
Part Number: LM5155

Tool/software:

Hi!
I have designed a PCB using LM5155DSSR and now during testing when we apply 36V on input, our MOSFET Q3 get damaged. 

after we removed Q3, and testing boost converter. We are getting 36V on TP7 (expected 150V) 

I am attaching the schematics diagram. I am not finding any issues in design and also was verfied by ti support before. stil you may be able to provide some help. 

Thank you

4135.Power Amplifier.pdf

  • 0
    TI__Genius 15945 points

    Hi Faiz,

    Thanks for reaching out. In your schematic i dont see the connection between LM5155 and the LMG device, to which Q3 is connected.

    Can you please explain this?

    Best regards

    Moritz

  • 0 in reply to Moritz
    Prodigy 115 points

    yes, there is no connection. but I am also confused why it happend. It's just output of LM5155 is giong to MOSFETs connected to LMG. 

  • 0 in reply to Faiz Majeed
    TI__Genius 15945 points

    Hi Faiz,

    Then you should open a new thread and mention the LMG device instead of LM5155.

    Thanks and best regards

    Moritz

  • 0 in reply to Moritz
    Prodigy 115 points

    ok, but can i get a guide whey LM5155 is not generating 150 V? because we disabeld LMG device and first checking on boost converter circuit. 
    I figured out previous issue and i found some problem in 5V converter circuit and beleive it damaged LMG device as well. so now I am testing on new pcb. 
    Thank you

  • 0 in reply to Faiz Majeed
    TI__Guru 58641 points

    Hi Faiz,

    I think there was some confusion generated by the usage of the different components on the PCB - esp. the reference to the LMG device.

    So, if I understood right we are only talking about the LM5155 circuit now. Please correct me if one of the below statements is not correct.

    This is tested on a new PCB where the additional circuit is removed.

    -> If not please separate this and check each part of the circuit first independent of the other.

    For the LM5155 circuit you said that Q3 got damage. After replacing it worked again?

    If it fails does if fail immediately does the voltage first increase for a short time?

    What is the QRR of the Diode D1?

    Best regards,

     Stefan