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TPS3809: TPS3809L30DBVR /RESET pin delay time issue

Paul Yeh
Genius 14095 points
Part Number: TPS3809
Other Parts Discussed in Thread: TPS3840, , TLV809E, TPS3870-Q1

Hi team,

In my customer's design, there are 5% TPS3809L30DBVR components can not  work normally with correct delay time.

In our datasheet, the delay time should meet the spec 120~280 ms.

Below waveform is customer's failure waveform for your reference.

CH3: VDD

CH2: /RESET

And I also attach customer's circuit for your double check.

Thanks

  • 0
    TI__Genius 9375 points

    Paul,

    Have you tried to test the circuit without the additional circuitry (inductor on VDD, 1k pullup on reset?) My thoughts are that this may be occurring due to your pullup on a push-pull device.

    Thanks,

    Abhinav.

  • 0 in reply to Abhinav.Sharma
    TI__Genius 14095 points

    Abhinav,

    From customer's testing result, they mentioned even they remove 1kohm pullup resistor, the failure symptom is still existed.

    But two way can solve this issue.

    1. increase 47ohm can solve this no delay issue

    2. And if they disconnect trace to MCU, our part will have delay. but this is impossible because this reset signal is for MCU usage.

    So any idea so far.

    Thanks

  • 0 in reply to Paul Yeh
    TI__Genius 9375 points

    Paul,

    For 1. If you increase this series resistor, how does this solve the delay? What value are you increasing to? I'm guessing this is fixing a leakage path.

    Thanks,

    Abhinav.

  • 0 in reply to Abhinav.Sharma
    TI__Genius 14095 points

    Abhinav,

    I wrote analysis report to tell you currently my finding in customer's system board.

    And I think the issue may cause by one pulse voltage induced from MCU's GPIO. But I don't understand why this pulse will impact RESET pin operation.

    It really need your expertise to figure out the root cause.

    ThanksRESET no delay issue.pdf

  • 0 in reply to Paul Yeh
    TI__Genius 9375 points

    Hi Paul,

    This is intended behavior and occurs because of Vpor(power-on-reset). This isn't detailed well in the TPS3809 datasheet, but you can take a look at the TLV809E or TPS3840 for Vpor description. This is an unavoidable pulse that details the minimum Vdd at which the output state is controlled. For the TPS3809, we detail below 1.1V as undefined, which is probably why you are seeing a pulse as high as 1V

    Thanks,
    Abhinav.

  • 0 in reply to Abhinav.Sharma
    TI__Genius 14095 points

    Abhinav,

    Thanks for your feedback. So do yo have any suggestion to solve this issue based on this situation?

    BRs

  • 0 in reply to Paul Yeh
    TI__Genius 9375 points

    Paul,

    If you want to completely eliminate Vpor, you should consider using an active-high device with overvoltage detection. In this case, the device will essentially always be in a fault state and thus output high until you need it to show low, when it technically exits a fault state and shows a low signal. This can be achieved, for example, with a device such as the TPS3870-Q1.

    Conversely, if the customer is okay with managing the Vpor as they have above with a resistor, they can do this as well.

    Thanks,

    Abhinav.