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LM5116MHX short circuit hiccup problem

DONG ZHENG
Prodigy 95 points
Other Parts Discussed in Thread: LM5116

Hi, TI expert!

I have been using LM5116MHX to make two BUCK power sources recently. The input voltage is 18-60vdc, and the output voltage is 5V 4A and 12V 3A.Products in the output short circuit test, low and high voltage input voltage point short circuit can be normal burp;A short circuit at the intermediate input voltage point can't burp, and the measured output current is the current limiting point, which will cause the MOS tube and transformer to get hot.I have debugged Cramp, Css, Rs and other parameters, but the effect is not so good. The comparison figure is as follows:

 60v input, 12V output 4A, output short circuit waveform as shown below, can normally burp.

55V input, 12V output 4A, output short circuit waveform as shown below, not normal burp.The average current is equal to the overcurrent limiting point current

In order to ensure the full input voltage range, output short circuit when the product works in burp mode, how to debug?

  • 0
    TI__Genius 11040 points
    Hello,

    Thank you for your detailed description and the scope waveforms? Could you also share the schematic for the dual LM5116 design?

    If I understand you correctly, the first waveform is showing a normal hiccup performance and the second image is showing the waveform of the second switch node which is not entering current limit. Is this correct?

    Thank you,
    Katelyn
  • 0 in reply to Katelyn Wiggenhorn
    Prodigy 95 points

    Hello,Katelyn!

    There may be a little problem with your understanding. Both waveforms can limit the current, but the second waveform does not limit the current in the right way.I mean LM5116MHX should enter the burp mode (continuous opening and restart) when the current limiting point or short circuit is reached. The problem I want to solve is how to debug the product so that the chip can enter the burp mode (continuous opening and restart) when the current limiting or short circuit occurs at any point in the design input voltage range.The advantage of this is that the temperature rise of MOS tube and BUCK inductor is in the safe area when short-circuiting for a long time.I have according to the basic WEBENCH ® design tools recommended tuning parameters but still can't solve;The attachment below is my schematic diagram. Could you help me analyze this problem in detail?Looking forward to your reply as soon as possible, thank you very much!YOGO_POWER_V0.pdf

  • 0 in reply to DONG ZHENG
    TI__Genius 11040 points
    Hello,

    Thank you for sharing additional details and helping to answer my questions.

    From your explanation, it seems as though the current limit is not being hit when the input voltage is in a certain range. What is the output voltage when the short circuit protection is not working? Also, do you have the same problem with U3 and U1?

    One way to monitor if the device is entering current limit is to measure the voltage at the UVLO pin. If the device is in current limit, this voltage should be pulled low to 200mV. Could you check if this device is not entering current limit at certain voltages? If so, we can trying adding a resistor to set the current limit as described in pages 16-17 of the datasheet.

    Thank you,
    Katelyn
  • 0 in reply to Katelyn Wiggenhorn
    TI__Genius 11040 points
    Hello,

    I want to follow up regarding this thread. Would you be able to answer a couple of follow up questions below?


    From your explanation, it seems as though the current limit is not being hit when the input voltage is in a certain range. What is the output voltage when the short circuit protection is not working? Also, do you have the same problem with U3 and U1?

    One way to monitor if the device is entering current limit is to measure the voltage at the UVLO pin. If the device is in current limit, this voltage should be pulled low to 200mV. Could you check if this device is not entering current limit at certain voltages? If so, we can trying adding a resistor to set the current limit as described in pages 16-17 of the datasheet.

    Thank you,
    Katelyn
  • 0 in reply to Katelyn Wiggenhorn
    TI__Genius 11040 points
    Hello,

    Due to inactivity, I am going to close this thread. Please response to this thread if you have additional follow up questions or information.

    Best Regards,
    Katelyn