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LM5155: Boost converting not boosting

William Van Raemdonck
Prodigy 10 points
Part Number: LM5155

Tool/software:

Hi, 

I'm using this converter to boost 5V to 30V.

But when I measure the output unloaded I get 8.5V on the output.
When I load it with a 1K ohm resistor it collapses to 5V.

I double checked the datasheet but can't immediately find anything wrong.

Any guess on what could be the problem.
I have 5 pcbs all with the same problem, so I'm pretty sure it isn't a solder problem.

Thank you in advance,

William
6646.pdf
  • 0
    TI__Genius 16115 points

    Hi William, 

    Thanks for reaching out. 

    The Webench schematic looks ok. Can you also send the actual schematic you built as well as the output current spec?

    Can you please also share some scopeshots of Vin, Vout , switchnode and CS pin in no-load and loaded condition?

    Thanks and best regards

    Moritz

  • 0 in reply to Moritz
    Prodigy 10 points

    Hi,
    Yes I rated the system for 1A in normal operation I expect to pull around 500mA peak.

    VCS Unloaded:





    VCS Loaded:

    Vin Unloaded:


    Vin Loaded:


    Vout Unloaded:


    Vout Loaded:


    Vsw Unloaded:

    Vsw Loaded:


    Schematic:

    0285.pdf

    I don't know if the quality of the image is good enough but I included it in this pdf as well.

    Its a first time for me working with boost converters, but my left toe presumes Vsw isn't supposed to look like that.

    Kind regards,

    William

  • 0 in reply to William Van Raemdonck
    Prodigy 10 points

    I see something went wrong with the formatting this is the order of the images

    VCS Unloaded

    VCS Loaded

    Vin Unloaded

    Vin Loaded

    Vout Unloaded

    Vout Loaded

    Vsw Unloaded

    Vsw Loaded

    Schematic