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TCA9517-Q1: Enable input potential System failure

Zachary Massicotte
Prodigy 10 points
Part Number: TCA9517-Q1


Hi, 

In the datasheet it is stated that "the EN input should only change state when the global bus and repeater port are in an idle state, to prevent system failures".

In the event that either the global bus AND/OR the repeater ports were being driven while the EN input changed state, how would this system failure present itself, what does this system failure mean exactly?

Regards,

Zachary

  • 0
    TI__Guru 54558 points

    Hi Zachary,

    When EN pin is LOW, the TCA9517-Q1 buffer re-drivers are off. The TCA9517-Q1 will not re-drive a LOW from one side to the other. 

    When EN pin is HIGH, the TCA9517-Q1 will look for a logic LOW and will re-drive it to the output. If there is existing I2C communication on either side of the buffer when EN pin is set HIGH, the buffer will begin transmitting I2C to the output side (whichever that is) which may put the connected target/controller devices into an unknown state. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Prodigy 10 points

    Thanks Tyler,

    I'd just like to explicitly clarify what does the datasheet mean by "System Failure"

    Regards,

    Zachary

  • +1 in reply to Zachary Massicotte
    TI__Guru 54558 points

    Hi Zachary,

    A system level failure could be a stuck I2C target that mis-interpreted the I2C data frame because it saw SDA/SCL after TCA9517-Q1 was EN during the communication. 

    Regards,

    Tyler