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TCA9545A: Vcc rising time

Yusuke Mukuno
Expert 7395 points
Part Number: TCA9545A

Hi

Regarding VCC_FT in the datasheet table3 Recommended Supply Sequencing And Ramp Rates.

Vcc_FT : 1ms to 10ms

However, customer measurement results was 0.7ms by customer circuit configuration.

What concern do you have about firster Vcc rising?

Thanks

Muk

  • 0
    TI__Guru 73471 points

    Hey Muk-san,

    If you are planning on powering down and then quickly powering back up the device like in figure 20 of the datasheet then you run the possibility that when you power up, the POR does not properly trigger and the device could power up in an unknown state.

    If your fall time is 0.7ms and you then power and let it unpowered for several seconds (assuming Vcc decays all the way down to GND) then power up and meet the power up requirements then you wouldn't expect the issue of a bad POR to occur. That fall time requirement is only if you plan to quickly power cycle.

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 40 points

    Dear Bobby

    I’m inoue.

    Thank you for answer.

    I have additional two questions.

    1) The power off period is set to 100ms in actual use. Is there any problem?

    2) If the fall time is not satisfactory (less than 1ms),
        What is the minimum time of the power off period?

    Inoue

  • 0 in reply to user5865991
    TI__Guru 73471 points

    Hey Inoue-san,

    "1) The power off period is set to 100ms in actual use. Is there any problem?

    2) If the fall time is not satisfactory (less than 1ms),
        What is the minimum time of the power off period?"

    Ideally what we want is to have the Vcc pin go to GND. If the Vcc pin reaches GND in 100ms, then I believe this is fine. (The 100ms is longer than the Vcc_TRR time of 40us). I assume a few microseconds at GND would be a sufficient power off time.

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 40 points

    Dear Bobby

    Thank you for answer.

    -Inoue