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TPS61391: About Reference design PMP40871

teritama
Expert 2165 points
Part Number: TPS61391
Other Parts Discussed in Thread: PMP40871, , TPS7A4101

Tool/software:

Hi team,

Our customer use TPS61391 follow PMP40871. And they are concerned about when input of this circuit is hot-swaped, it is possible or not input voltage increase above absolute rate by input pin become open.

Do you have any information about like this case?

We think if it is possible, it should be fine if use protection debice whitch have internal discharge pass on power pass like efuse on TPS61391 input.

Best regards,

teritama

  • 0
    TI__Mastermind 18940 points

    Hi Teritama,

    There is do risk of high spike at Vin in hot-swaped, especially when the Vin trace from the Vin supply to the Vin pin is very long.

    Usually a 47μF or 100μF input electrolytic capacitor provides good protection.

    If the hot-swaped is frequent, then as you said, adding e-fuse or TVS will have better protection.

    Regards

    Lei

  • 0 in reply to Lei Zhong
    Expert 2165 points

    Hi Lei-san,

    Thank you for your reply. I understand, about input spike, we suggested to the customer to use efuse. It seems to be protected.
    We have one more question.
    If TPS61391 and TPS7A4101 are controlled by same enable signal. When disable, I think it is possible the out put capacitor discharge reverce current to TPS7A4101 input and increace TPS7A4101 input voltage above 60V.
    I want to your opinion about above. Is it recommended to add input capacitor?
    Best regards,

    teritama

  • 0 in reply to teritama
    TI__Mastermind 18940 points

    Hi Teritama,

    As my understanding, when both the TPS61391 and TPS7A4101 are disabled, the IN and OUT of the TPS7A4101 will be isolated, and the TPS61391 output energy will be stored at the output caps, and the TPS61391 Vout gradually decrease to 0 since the energy consumed by the leakage and the feedback resistors. There will be no risk that TPS7A4101 input voltage rises above 60V. 

    Just let me know if I have any wrong understandings.

    Regards

    Lei

  • 0 in reply to Lei Zhong
    Expert 2165 points

    Hi Lei-san、


    When TPS7A4101 output capacitor is 20uF and no load resistor, after both device disabled, in my understanding TPS7A4101 input voltage is falling faster than output voltage.
    Then the output voltage is larger than input voltage, so I expect to occure reverse current pass TPS7A4101 body diode.
    We concerned about this cause input voltage increase.

    Best regards,

    teritama

  • 0 in reply to teritama
    TI__Mastermind 18940 points

    Hi Teritama,

    Understand. Thanks for your explanation.

    I think when both the devices are disabled, the max voltage at the TPS7A4101 input won't be higher than that when the two devices are working.

    As long as the TPS7A4101 Vin is higher than the Vout, the body-diode will block the reverse current.

    Regards

    Lei