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LM25118: Not working properly

user6543879
Prodigy 30 points
Part Number: LM25118

I refer to a lm25118 adjustable output application circuit designed by datasheet, but it failed. I hope the engineer can point out the problem for me. Thank you. His problem is that he can only output a voltage of no more than 3.4V, and there is no response when he is loaded.

  • 0
    TI__Guru* 78190 points

    Hi, 

    Thank you for posting.  Could you tell what is the input voltage?  What are RP1 and RP2 setting value? 


    Thanks,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Prodigy 30 points

    Hello, thank you very much for helping me.

    My input voltage is 6v-30v.

    RP1 uses 10K

    RP2 uses 10K

  • 0 in reply to user6543879
    TI__Guru 65280 points

    Hello user6543879,

    So at the moment the set output voltage is 13.5V. How much load do you want to drive?

    Please check if the behavior changes when you add 10uF ceramic caps on the input and output.

    You mention that the input voltage starts at 6V. In your schematic the UVLO threshold is set to 8V.

    Please check as well if increasing C2 or reducsing C1 helps.

  • 0 in reply to Brigitte
    Prodigy 30 points

    Hello, thank you very much for answering my question

    I would like to ask how to calculate the output voltage to facilitate my future design

    In addition, when the input voltage is greater than 8V, the power supply does not respond

    It has been modified according to your method, but there is no response

    I think there may be a major error in the schematic diagram. Could you help me to correct it

  • 0 in reply to user6543879
    TI__Guru 65280 points

    Hello usesr643879,

    A good design starting point is the quick start calculator: 

    I cannot find a major issue in your schematic. It is drawn not very clear, but the components seem to be connected as needed.

    But a power supply can not work, even if the schematic is correct, as it is as well dependent on layout. E.g. I do not expect that this stops the part from operation, but you did not connect the power pad of the device. It is recommended to connect it to GND.

    Do you possibly have a second board to check if this behaves the same?

    Please check if you have all components connected as given in the schematic.

  • 0 in reply to Brigitte
    TI__Guru 65280 points

    Hello usesr643879,

    As there is no answer from you, I expect that you have been able to solve your issue and will close this thread now. If this is not the case, please post below or create a new thread, if this one is already locked.