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TCA9617B: startup Back curve of TCA9617B

Frank Xiao
Genius 12055 points
Part Number: TCA9617B
Other Parts Discussed in Thread: TCA9802

Hi team,

My customer is using the TCA9617B now. We want to check how to improve or eliminate the phenomenon. We have tried to increase the pull up resistor value, but seems not to improve too much.  Do you have more suggestions? Thanks.

1.2K pull up resistor

2.2K pull up resistor

4.7K pull up resistor

  • 0
    TI__Guru 62920 points

    Hi Frank,

    This is a side effect of the buffer implementation used in the device, which uses a static voltage offset on the B side in order to set its "VOL" higher than its "VIL."  This helps to support bidirectional communication since it allows for the buffer to handle different "low" signals that it drives itself versus "low" signals driven by other I2C devices on that bus segment.  You can read more about this type of buffer in this app note:

    http://www.ti.com/lit/pdf/SCPA054

    The behavior generally should not cause issues as long as the "pedestal" amplitude is low enough to be considered logic-low by all devices on that segment.  Is the customer seeing any issues with data errors?

    Regards,
    Max

  • 0 in reply to Miguel Robertson
    TI__Genius 12055 points

    Hi Max,

    Thanks for your reply. We have other devices on the I2C link. Which the Vil is different as TCA9617B, their ViL spec can be 0.3v~0.9v, How to deal with the condition? Or do we have other device to solve the issue? Thanks.

  • 0 in reply to Frank Xiao
    TI__Guru 62920 points

    Hi Frank,

    Since the TCA9617B B side VOL is larger by design, it cannot be lowered significantly through external circuits (like pull-up resistances).  Is it possible to swap the orientation of the buffer so that the A side interfaces to the devices requiring lower VOL?  If not, another part number could be used.  TCA9802 is often used in applications requiring lower voltages since it uses a different buffer architecture that does not require a static voltage offset.

    Also note that we have a design tool that can help recommend I2C components based on the specifications of the different I2C master/peripheral devices that need to communicate on a bus.  You can find it here:

    Regards,
    Max