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Original question:

TPS63700: Overcurrent Protection Issue

TPS63700: TPS63700 startup issue

Udhayakumar Mahendiran
Prodigy 240 points
Part Number: TPS63700


Hi,

    I am using TPS63700 for -5V supply from 5V. Sometimes the converter gives no output, having a random behavior that sometimes it is working fine. I suspect there is a pre-biased output condition. Does this converter supports prebiased startup? if not how to overcome this condition.?

  • 0
    Prodigy 240 points

    Hi,

         Here is the output waveform at OUT pin. It seems that sometimes when input of 5V given, output goes low at first and suddenly it come backs to 0V. Other times it is working as expected.

    Here I have attached the schematic. Schematic seems ok. The Output capacitors are 4 x 4.7uF but in schematic it is mentioned wrong. I have added more capacitance at the output then also same issue. Anything need to be done with feed forward capacitor?

  • 0 in reply to Udhayakumar Mahendiran
    TI__Guru 67755 points

    Hello Udhayakumar Mahendiran,

    According to the measurement you show, the output is not pre-biased when the problem occurs. The schematic looks exactly like Figure 2 in the datasheet, with different output capacitors. You mentioned that you use 4*4.7uF output capacitors instead of the 4*4.7nF given in the datasheet, so this is then exactly Figure 2 in the datasheet.

    As you mention that the issue is happening randomly, it will be difficult to dig into the details without more measurements. Would it be possible for you to check the different pin voltages during a normal startup as well as a startup where the converter does not start, to get an idea what is different in these cases?

  • 0 in reply to Brigitte
    Prodigy 240 points
    Hi Brigitte,

    Thank you for your response. I have changed the capacitor C100 to 22uF. I didn't try with other values. Seems it solved the problem. I did power reset for 20 times and it seems ok now and giving output. I will check more times to confirm. Anyway if adding a capacitor at enable pin solved problem means what is the reason behind it? I would like to know.
  • 0 in reply to Udhayakumar Mahendiran
    TI__Guru 67755 points

    Hello Udhayakumar Mahendiran,

    For giving an answer to your question, it would be necessary to see the different in voltage on VIN and IN during the problem as well as when the bigger cap is attached to C100. 

  • 0 in reply to Brigitte
    TI__Guru 67755 points
    Hello Udhayakumar Mahendiran,

    I haven’t heard back so I’m assuming you were able to resolve your issue. If not, just post a reply below (or create a new thread if the thread has locked due to time-out).