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SN74LVC2T45 Question about power sequece.

na na78
Guru 16770 points

Hi

We know following power sequence is recommended.
-Connect ground before supply voltage is applied.
-Power up Vcca.
-Vccb can be ramped up along with or afte Vcca.

We have following questions.

1. There is a possibility that Vccb is powered down after the system start (Vcca is still applied) and then Vccb is applied again. Are there any problems?

2. Are there any rules of powering up/down timing between Vcca and Vccb? (e.g. Vccb should be applied as soon as possible after Vcca is applied.)

regards

  • 0
    TI__Genius 16510 points

    Hello Na na,

    You should not have any issues, since the device should trigger a POR on itself. This assumes that your VCCB rail will go all the way to 0V for at least several ms before ramping back up.

    2) There are not with this device for powering up. Powering down, if only 1 rail is going low, it should go all the way to 0V and stay for a short amount of time (a few ms is fine) and then power up. This is a recommendation to make sure the device successfully has a POR.

  • 0 in reply to Jonathan Valdez
    Guru 16770 points
    Hi Jonathan

    Thank you for you reply.

    Can we confirm your answer?

    1) You should not have any issues, since the device should trigger a POR on itself. This assumes that your VCCB rail will go all the way to 0V for at least several ms before ramping back up.
    ->The operation we showed has no problem, doesn't it?
    We couldn't find POR function in datasheet. What is a POR operation?

    2) There are not with this device for powering up. Powering down, if only 1 rail is going low, it should go all the way to 0V and stay for a short amount of time (a few ms is fine) and then power up. This is a recommendation to make sure the device successfully has a POR.
    -> We can't get the word "all the way to 0V". What does it go to 0V?

    regards
  • 0 in reply to na na78
    TI__Genius 16510 points
    Hello Na na,

    1) The device will undergo a reset function internally. This occurs when the power is ramped up. It is automatic and you do not have to worry about it.

    2) the VCCB should go to 0V before going up to VCCB voltage again.