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Original question:

TXS0102: Multiple I2C devices

TXS0102: I2C interface to only 2 slave devices

Antenna_Head
Genius 11395 points
Part Number: TXS0102

Customer has FPGA w/1.8V I2C bus, needs to interface to a pair of 5V powered I2C slave devices,  SCLK = 1 MHz.

Any issues using TXS0102 in this secenario?  The pair of slaves obviously have different addresses and should not contend.  Another thread on this topic mentioned this should be OK so long as loading is < 70 pF on the line.  

This particular board is rather small, so not anticipating traces adding much capacitance.

Also, would like to rely on the built-in pull-up resistors in the device instead of placing additional I2C pull-ups.  Is this OK as well?  Seems like 10K would be fine to maintain the bus, and the edge-accelerators can keep the edges clean.

Seems like this will work fine, Please confirm.

Thanks, Best, Steve

  • 0
    Guru 244220 points

    Yes, this should work.

    (You actually have two 10 kΩ pull-ups in parallel.)

  • 0 in reply to Clemens Ladisch
    TI__Genius 11395 points

    Clemens-

    I'm not so sure; the data sheet doesn't really specify the loading except for Figures 4 and 5 in the "Parameter Measurement Section", and there it is only 15 pF.  Two loads could easily amount to 10 pF, and not hard to incur at least 5 pF through traces.  


    I do think it will work, but we need to have better quantitative analysis or specs to go on.

    Need more guidance from the product line on this topic.  

  • 0 in reply to Antenna_Head
    TI__Guru 56100 points

    Hi Antenna,

    The TXS should handle this frequency and support the loading. You are right about the PMi section where the loading is given according to which the electrical / timing specs are measured.

    If its possible to lower the trace length and/or trace cap it would also help.

    The TXS should also have a slight margin on the specs to support the data rate.