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WEBENCH® Tools/LM5118: Load problem of lm5118

user6234651
Prodigy 20 points
Part Number: LM5118

Tool/software: WEBENCH® Design Tools

i use lm5118.I hope the output of the circuit board is 12V 3a，input is 10v，The circuit diagram is from WEBENCH，When I add a 6 ohm or less load, the output voltage drops，and The waveform of UVLO pin fluctuates up and down at 1.25V,

Wave form of UVLO When I add a load of 6 ohms

Wave form of inductance When I add a load of 6 ohms

Wave form of inductance When I add a load of 8 ohms

I found this to be similar to the hiccups on page 18 of the datasheet。But the load current doesn't seem to be that big

I hope I can get a solution to improve the output power. Thank you

  • 0
    TI__Mastermind 21720 points

    Hello User6235651

    Thanks for reaching out with your question and for using the LM5118.

    Based on your UVLO waveform can it looks like the peak current limit is being triggered. After using the LM5118 quick-start calculator it looks like the control loop might not be stable. This could be causing the inductor current to swing into peak current limit.

    The output capacitance looks small for this design at 15uF. Does this match the value the WEBENCH supplied?

    Please let me know if you have any questions.

    Thanks,

    Garrett

  • 0 in reply to Garrett Roecker
    Prodigy 20 points

    Thank you for your reply. In fact, the output capacitance is 680uF and 100nf.No load is normal,Other components are the same as the WEBENCH, except for the input and output capacitors

    So how can I avoid this？

  • 0 in reply to user6234651
    TI__Mastermind 21720 points

    Hello,

    I would recommend adding an RC filter the current sense signal. This will help to filter out some noise that might be getting injected on the signal.

    the other suggestion is to decrease the value of the current sense resistor to 12mOhm or 13mOhm.

    Thanks,

    Garrett