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LM5116: Short circuit at startup

Timon Achtnich
Intellectual 555 points
Part Number: LM5116


Hi

I am working with the LM5116 on several boards successfully. However on one board the LM5116 creates sometimes a short circuit at startup.

The signals in the following Oscilloscope screenshots are as follows:

yellow: Enable (Pin 4 EN)

blue: Gate Low (Pin 15 LO)

red: Gate High (Pin 19 HO)

Below you see a screen shot of the startup sequence (EN goes from low to high) when the system is working properly afterwards.

Below you see a screen shot of the startup sequence (EN goes from low to high) when the system is generating a short circuit and the system goes into reset. The high side switch and the low side switch are high at the same time point.

The schematics is as follows:

An the layout:

We already exchanged the LM5116 but we still have the same effect. How can this hapen and how can we overcome this short circuit situation?

Timon

  • 0
    TI__Mastermind 35210 points

    Hello,

    I am looking into this but would like to talk to product definer first.

    Please give me a day or two to follow up.

    Thanks.

  • 0 in reply to Marshall_Beck
    TI__Mastermind 35210 points

    Sorry for delay.

    Can you please reduce the value of Css (C1324) to 22nF and re-run experiment?

  • 0 in reply to Marshall_Beck
    Intellectual 555 points

    Hi Marshall,

    We have redcuced Css to 100 nF but still face the same issue. I do not think that reducing Css to 22 nF will solve the problem. Do you have any other idea to solve this problem?

    Kind regards,

    Timon

  • 0 in reply to Timon Achtnich
    TI__Mastermind 35210 points

    Hello Timon,

    Can you try the following:

    1. Re run experiment with 22nF

    2. You can also try with higher output capacitor, say 100uF electrolytic (just for experiment)

    If my suspicion is correct either should aid in eliminating the issue.

  • 0 in reply to Marshall_Beck
    Prodigy 40 points

    Hello Marshall,

    I am Timon's colleague and I tested your proposition:

    - First test:  with the 22 nF capacitor on the Softstart Pin

    - Second test: additionally with the 100 uF electrolytic on the output.

    Unfortunately, these changes did not help eliminating the issue. Are there other potential solutions we could test to solve this?

    Thank you for your answer!

    Kind regards

    Emil

  • 0 in reply to Emile Décosterd
    TI__Mastermind 35210 points

    Hello Emil,

    Thanks for sharing the outcome from the experiment.

    What is your programmed output voltage?

    What is the load condition during startup?

    Since, increasing soft-start current and soft-start time did not impact the result, could you please run one more experiment:

    Could you try running the same experiment again, increasing the load condition during startup, from half to full load, seeing if increasing loaded condition will impact result?

    My assumption is it will, but we will see :)

    Please let me know if you can do this.

  • 0 in reply to Marshall_Beck
    Prodigy 40 points

    Hello Marshall,

    The programmed output voltage is 16 V and the load condition during startup is approximately 32 mA. We ran an experiment with a load current of 150 mA but did not see any improvement.

    The weird thing is that this design works well on other boards, this is the first one not working. Are there other factors than the passive elements that could prevent the LM5116 from working properly? We already replaced the chip but this did not solve the issue.

    Thanks again for your support.

    Kind regards,

    Emil

  • 0 in reply to Emile Décosterd
    TI__Mastermind 35210 points

    Hello Emil,

    Passive elements variation was to understand problem at hand. Could possibly allow for potential fix, though experiments that you ran were to identify the problem more or less.

    Could you please contact me at m-beck1@ti.com