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TCA9517: TCA9517 application

Nanfang Liao
Intellectual 2085 points
Part Number: TCA9517

Hello Team,

My customer uses our 2pcs TCA9517, for some special reason, there are 1k pull-up and 1k pull-down resistors at B side SDA signal for 1st TCA9517, you can check the application as below. Does this design impact I2C work for 2nd TCA9517? thanks

Regards,

Nanfang

  • 0
    TI__Genius 17215 points
    Hello Nanfang,
    This won't work! This is an open drain communication protocol. The voltage will never get above half the voltage. What are they trying to accomplish? I can recommend a circuit that might work.
    -Francis Houde
  • 0 in reply to fhoude
    TI__Intellectual 2085 points
    Hello Francis,

    Thanks for your quick response. The first pcs TCA9517 SDA is a fixed voltage 1.65V, and our TCA9517 is a buffer part, why it impact 2nd pcs TCA9517I2C work? Can you help to give more detail expalanation?

    Regards,
    Nanfang
  • 0 in reply to Nanfang Liao
    TI__Genius 17215 points

    Hello Nanfang,

    I don't understand what you are trying to do in this design?  What are you trying to accomplish?  Why would you put a resistor divider on the SDA line of the B side????   Why is there a "NC", assuming you mean No Connect? 

    I don't understand what you mean by SDA fixed at 1.65, other than it being a resistor divider??? Is the SDA not connected to a device and meant to be left floating?  Please explain what they are trying to do.  A block level diagram or schematic might shed some light for me on what is trying to be done.

    -Francis Houde

  • 0 in reply to fhoude
    TI__Intellectual 2085 points
    Hello Francis,

    Customer has some special reason, they need to put a resistor divider on the SDA line of the B side, and there is no connection of the B side, so it is fixed at 1.65V. Because there is no connection of the B side, so i think it should not impact the communication between I2C master and I2C slave through 2nd 9517, what's your opinion? Thanks

    Regards,
    Nanfang
  • 0 in reply to Nanfang Liao
    TI__Genius 17215 points
    Hello Nanfang,
    Assuming they aren't using the B side of the TCA9517 with the resistor divider then it shouldn't affect the A side. You really should understand why they are doing this. You need to be more curious about these things, it helps you understand their system and implementation. The better you understand their application and implementation the better you can support them.
    -Francis Houde
  • 0 in reply to fhoude
    TI__Genius 17215 points
    Nanfang,
    One more thing. I would have them place pull up the SCL line on the B side with a weak pull up resistor. Just in case there is leakage that could pull down that node to ground. That could adversely affect the I2C communications.
    -Francis Houde