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LM5122: LM5122MH design in problem

bob chen
Prodigy 30 points
Part Number: LM5122

Hi Sir,

I have already designed in the LM5122 schematic fully based on the reference "Design : 198 LM5122MH/NOPB" from TI's engineer but the actual pc-board can NOT step up to dc100V properly under no load.In fact,when power up with Vin=10Vdc then the system is with Vout=10Vdc only under no load, the expected boost function is not active obviously!

WEBENCH ® Design Report
Design : 198 LM5122MH/NOPB
LM5122MH/NOPB 5V-30V to 100.00V @ 0.1A
VinMin = 5.0V
VinMax = 30.0V
Vout = 100.0V
Iout = 0.1A
Device = LM5122MH/NOPB
Topology = Boost
Created = 2022-07-14 11:05:35.467
BOM Cost = NA
BOM Count = 26

Below is my schematic.

Please kindly help to point out what's the root-cause of the boosting failure.

Appreciated so much.

Bob Chen 2023/6/13

  • 0
    TI__Genius 11215 points

    Hello, 

    Thanks for reaching out. Is there any condition of Vin and load at which you can see the correct output voltage? 

    Kind regards,
    EM

  • 0 in reply to EM
    Prodigy 30 points

    Hello EM,

    No! The Vout always keeps almost the same voltage as the Vin under no load condition.

    I have checked the UVLO pin voltage which is 2.7V, it's much greater than 1.2V, it should work with boost function.

    I also tried to pull up the UVLO pin voltage up to 10V(same as Vin) but the Vout was still with10V, without boost function.

    I can make sure all parts on board which are all under good soldering conditions with correct part values and correct polarities, I do wonder which points I should check.

    Please kindly guide me to find out the root cause, thanks a lot! 

    Best Regards,

    Bob Chen 2023/6/14

  • 0 in reply to bob chen
    Prodigy 30 points

    Hello EM,

    For the boost failure issue, do you have any further ideas for fixing?

    Please share with me, thanks so much.

    Best Regards,

    Bob Chen 2023/6/17 

  • 0 in reply to bob chen
    Prodigy 30 points

    Hello EM,

    Good day!

    For my boost function failure issue, do you have any ideas for fixing?

    Please kindly share with me, thank you very much.

    Best Regards,

    Bob Chen 2023/6/26

  • 0 in reply to bob chen
    TI__Genius 15545 points

    Hi Bob,

    Thanks for your reply. It seems like the highside MOSFET deos not have the right direction with respect to drain and source. Please have a look at the datasheet example/EVM and make sure that drain and source has the right direction. The MOSFET you are using might have been damaged, so we recommend to try with a new one.

    Best regards,

    Moritz