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LM66200: Short soft start time

Kaji@PAN
Mastermind 7775 points
Part Number: LM66200

Tool/software:

Hello,

I would like to ask you a question about the soft start of the LM66200.
The VOUT rise waveform was measured with VIN1 set to 3.3V and VIN2 set to 0V.
The VOUT rise time was 19us, which is quite short.
Are there any factors that cause the soft-start time to be so short?
Two 10uF capacitors are connected to VOUT.

Best regards,

  • 0
    TI__Mastermind 46370 points

    Hi Kaji,

    Can you repeat the test with lower voltage as well, something like 1.8V

    Regards,

    Shiven Dhir

  • 0 in reply to Shiven Dhir
    Mastermind 7775 points

    Thank you for your reply.
    I set the voltage to 1.8V and measured again, but the result was the same, and the soft start time remained unchanged.
    I am also concerned about the lack of a delay time.
    Is this symptom caused by a malfunction? Or is it something that is caused by the circuit configuration?
    Best regards,

  • 0 in reply to Kaji@PAN
    TI__Mastermind 46370 points

    Hi Kaji,

    To verify if its malfunction, can you replace the IC and test?

    Regards,

    Shiven Dhir

  • 0 in reply to Shiven Dhir
    Mastermind 7775 points

    Thank you for your reply.

    I changed the IC and checked its operation, and found that it was working properly.
    When I checked the IC that was not working properly, I found that VIN1 and VOUT were shorted.
    In relation to this, I would like to ask you a follow-up question.
    In the waveform I attached the other day, you can see that the voltage undershoots when VIN1 rises.
    This undershoot seems to exceed the rated value.
    Is it possible that VIN1 undershoot could cause a short circuit between VIN1 and OUT?
    Regarding pin handling, the ST pin is open and the ON pin is connected to GND, but is this OK?
    Do these pins need to be pulled up or down with resistors?
    If you know of any other cases where VIN1 and VOUT could be shorted, please let me know.

    Best regards,

  • +1 in reply to Kaji@PAN
    TI__Mastermind 46370 points

    Hi Kaji,

    Violating the abs-max rating can damage the IC and VIN to VOUT short is possible.

    Leaving ST floating and ON grounded is fine.

    Regards,

    Shiven Dhir