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TCA9803: Current SINK Specification (diff in Sides A and B)?

Chris Yorkey
Genius 15855 points
Part Number: TCA9803
Other Parts Discussed in Thread: TCA9517

TI Friends & Family,

One of our customers has a unique application for the TCA9803 where they are transitioning from the older TCA9517 for longevity and cost reasons.  However, they need further information regarding the device datasheet specifications, particularly the current SINK spec.

The datasheet clearly identifies a current source spec (~3mA) and other forum posts suggests the current SINK spec is similar (although the TCA9517 was higher).

The question is, what is the official (or unofficial) Current SINK spec for the '9803 and also is there a difference between Sides A and B of the device which would also be applicable in this case?

Thanks for any input you can provide in advance.

Regards,

Chris

  • 0
    TI__Guru 73061 points

    "The question is, what is the official (or unofficial) Current SINK spec for the '9803"

    I'm not 100% sure on what you mean by sink spec.The TCA980x on B side requires that any slave driving low must have a driving strength of 150 ohms or less. For I2C compliant devices this should already be met as the I2C standard sets VoL to be 400mV at 3mA, this gives an RDSon of about 133 ohms. B side supplies its own current so it is designed to be able to sink its own current as well. No additional current should be added on B side (this means no external pull up resistors).

    "also is there a difference between Sides A and B of the device which would also be applicable in this case?"

    B side has its own current source and low dectection algorithm. Side A has more flexibility and only requires that the VoL be less than 30% of VccA to drive low. B side has restrictions such as not being able to be connected to any I2C switches/MUXes/level shfiters or any other static voltage offset buffer on their buffer side. It also does not want pull up resistors on B side since it supplies its own current source and uses that as a way to detect lows internally.

    -Bobby

  • 0 in reply to BOBBY
    TI__Genius 15855 points

    Hi Bobby,

    Thank you!  The clarification on the datasheet and the additional info you have added makes it clear that any external I2C device should be on the A side of the repeater.  That is where a user should be able to sink the current needed for the corresponding resistors.  

    Appreciate the clarification.

    Regards,

    Chris