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Original question:

TCA9800: can we change mater to SDA_B side

TCA9800: PU resistor on B side

dimitry chen
Expert 1145 points
Part Number: TCA9800
Other Parts Discussed in Thread: TCA9803, , TCA9802, TCA9509

Tool/software:

Hi 

My deign is VCCA =1V1 and VCCB=3v3

and the system have some extend device that cause PU on B side.

And I see the VIL in DS is (< 0.3 x VCCB)

I can confirm my system B side VIL is in spec ( < 0.3 X VCCB).

Does this mean my design is ok ?

  • 0
    TI__Mastermind 49958 points

    Hi Dimitry,

    Pull-up resistors cannot exist on B-side due to the internal current source of the device. The IEXT-I and IEXT-O must be satisfied at all times for the direction control of the buffer to work - passing LOW logic signals across the buffer in both directions during a point of contention. 

    It is recommended to remove these pull-up resistors on the B-side. IF stronger pull-up current is needed, consider moving to the TCA9803 which has stronger current drive to VCC. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Expert 1145 points

    Hi 

    Becuase side B have expansion slot like PCIE slot.

    We are not sure PU status on side B , and it have weak PU resistor like10K.

    Or do you have any other suggestion to replace TCA9800 ?

  • 0 in reply to dimitry chen
    Guru 317630 points

    You must not connect the TCA980x's B side to any circuit that might have a pull-up.

    But you could exchange the A and B sides.

  • +1 in reply to dimitry chen
    TI__Mastermind 49958 points

    Hi Dimitry,

    You can do according to what Clemens has suggested by switching A and B sides of the TCA9802. 

    Have you looked into the TCA9509? This device seems like it would be a better solution for your design. 

    No pull-ups can exist on A-side however. B-side pull-ups are allowed for TCA9509. 

    Regards,

    Tyler