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TCA6408A: Power sequence

Oba
Genius 17605 points
Part Number: TCA6408A


Hello,

Due to system power sequence requirement, I2C pull-up rail is powered up before VCCI and VCCP powering up.
It means SDA and SCL voltage is higher voltage than VCCI/VCCP.
From the datasheet input/output clamp current up to 20mA is allowed.

So is this condition allowed if SDA/SCL current is limited under 20mA?

Regars,
Oba

  • 0
    TI__Mastermind 24146 points
    Hello Oba,
    The pull up resistors should be referenced to the VCCI, why isn't it? Generally speaking you want to keep your SDA and SCL lines at a known state via the pull up resistor because the pins are considered inputs, and thus the general rule is to not let cmos input float or you could have shoot through current.

    The part is in a reset state when Vccp=0V. That means the SDA/SCL should be high z. You also have a pull up resistor that limits the current into the SDA/SCL lines. This should keep the current under that max allowed current.
    -Francis Houde