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SN65MLVD080: LVDS driver

John B
Intellectual 275 points
Part Number: SN65MLVD080
Other Parts Discussed in Thread: P82B96, P82B715, SN65LVDS049, SN65LVDS31, TIDA-060017

I am looking at the IC to convert single ended to differential because we think the length of the cable is too long for I2C. Therefore, we need to convert the clock and also data to differential. I was looking at the datasheet of SN65MLVD080. I am not sure if I get it completely. Is that the IC that can be used as LVDS transceiver ? that transform the single ended signal to differential. 

  • 0
    TI__Guru 58860 points

    Hi John,

    The I2C clock is unidirectional in most systems so it is possible to send that signal through a differential transceiver. 

    The dataline in I2C is bidirectional and any feedback loop would force the bus to lock up. It would not be a trival design to split the I2C bidirectional line into unidirectional lines using discrete methods. TI's portfolio has I2C cable drivers (P82B96 and P82B715) which can drive meter long cables. If you truly need to make the I2C signal differential (maybe for EMI concerns or for the noise immunity benefits) then you can take a look at this TI design: https://www.ti.com/lit/ug/tiduei0/tiduei0.pdf?ts=1711484136658&ref_url=https%253A%252F%252Fwww.google.com%252F

    -Bobby

  • 0
    TI__Genius 14681 points

    Hi John,

    Here is another application note that may be of use to you: 

    Transmitting SPI Over LVDS Interface Reference Design

    Regards, Amy

  • 0 in reply to Amy
    Intellectual 275 points

    Thanks for your reply. I understand that I2C clock is unidirectional that runs from I2C master to slave. And the I2C data is bidirectional between I2C master and slave. Both clock and data are single ended signals. 

    Using I2C cable drivers (P82B96 and P82B715) we can use longer length cable between I2C master and slave. How long it can be ? We have a requirement around 2 meter in one application and 5 meter in another application. 

    The I2C cable drivers (P82B96 and P82B715) does not convert single ended clock and single ended data into differential pairs, right ? I mean they don't convert them to one differential pair for clock and one differential for data. Please confirm. 

    Do we need the cable drivers at both ends, the I2C master and also at I2C slave ? 

  • 0 in reply to John B
    Guru 280000 points

    The I2C cable drivers allow you to use a bus with a total capacitance of more than 400 pF. The higher currents also reduce the noise sensitivity somewhat.

    The P82B96 splits the I2C lines into two unidirectional lines; this allows you to add differential transceivers in the middle.

    M-LVDS is overkill for point-to-point connections. Use plain 2+2 transceivers like the SN65LVDS049.

  • 0 in reply to Clemens Ladisch
    Intellectual 275 points

    Yes, I also think that we need to use LVDS differential transceivers for 5 meter long I2C cable. If we use SN65LVDS049, than we will then have differential clock (sclk_p, sclk_n) and differential data (sda_p, sda_n). That means in total there will be four wires (two differential pairs) in the cable between the I2C master and I2C slave board, right ? In total there will be two SN65LVDS049 in the design. One on the I2C master board and the other on the I2C slave board, right ?

    But before these transceivers SN65LVDS049, do we still need to use I2C cable drivers (P82B96 and P82B715) on each board ? 

  • 0 in reply to John B
    Guru 280000 points

    No; you have eight wires, four in each direction. (LVDS is unidirectional.)

    You need both SN65LVDS049 and P82B96. (The P82B715 would not be able to split the I2C signals into unidirectional lines.)

  • 0 in reply to John B
    TI__Genius 14681 points

    Hi John, 

    Check into using the SN65LVDS31/33 - Figure 2. TIDA-060017 Block Diagram in the application note utilizes this solution. 

    Transmitting SPI Over LVDS Interface Reference Design

    You can view other relevant files for this reference design here: TIDA-060017 reference design | TI.com, under the "Design Files & Products" section.

    Regards, Amy