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SN65MLVD206B: SN65MLVD206B load and output level

user6519235
Prodigy 220 points
Part Number: SN65MLVD206B

Tool/software:

Hi,
I have some question about using SN65MLVD206B.As shown in the figure below, the SN65MLVD206B is used for both the driver and receiver.
The M-LVDS is 100 ohm terminated. The M-LVDS line has an amplitude of 1.0 V on the P-side and 1.0 V on the N-side.
The amplitude seems to be large. Is there a problem?
Is there any problem with 100 ohm termination for M-LVDS line?

Best regards,
Hyodo

  • 0
    TI__Expert 3170 points

    Hi,

    M-LVDS is intended to be double terminated with 100 Ohm resistors to achieve an equivalent resistance of 50 Ohms. Please see this App Note for more details.

    Regards,

    Jack

  • 0 in reply to Jack Campbell
    Prodigy 220 points

    Hi,

    Thank you, and sorry for late reply.

    Is there anything I should be aware of when connecting only two devices with M-LVDS?
    The amplitude of the signal is higher than M-LVDS level.

    "M-LVDS is intended to be double terminated with 100 Ohm resistors "
    That means 100 Ohm termination is required for both transmitter and receiver?
    Currently, only the receiving end is terminated by 100 ohms.


  • 0 in reply to user6519235
    Guru 316780 points

    The differential voltage is higher than normal, but that is no problem for the receiver.

  • 0 in reply to user6519235
    TI__Expert 3170 points

    Hi,

    As Clemens said, the receiver can handle the higher differential voltage just fine as the Recommended Operating VID (max) is Vcc.

    The M-LVDS spec says that M-LVDS buses should use 50 Ohms of termination resistance. That is why the datasheet parameters for M-LVDS devices are given for a load resistance of 50 Ohms. Typically, best performance is realized when two 100 termination resistors are used in parallel as compared to a single 50 Ohm. In your case it looks like you are only doing point-to-point communication, not multipoint, so double termination might not be as critical. The only concern would be signal integrity if you are driving a 50 Ohm transmission line. Using a single 100 Ohm termination resistor will create more reflections than the matching 50 Ohm would. Depending on your datarate and layout, this might not be acceptable.

    Regards,

    Jack

  • 0 in reply to Jack Campbell
    Prodigy 220 points

    Hi, Jack
    Thank you for a more detailed answer.
    I understand that the current circuit is not a big problem.
    However, I would like to improve the waveform as there is an overshoot.
    I would like to change the terminating resistor. Which is better, a or b in the figure below?


    Best regards,
    Hyodo

  • 0 in reply to user6519235
    TI__Expert 3170 points

    Hi Hyodo,

    I would recommend option B (two 100 Ohms) as that is the typical topology for M-LVDS systems. One resistor should be as close to the driver as possible and the other should be as close to the receiver as possible.

    Regards,

    Jack

  • 0 in reply to Jack Campbell
    Prodigy 220 points

    Hi Jack,
    My guess turned out to be correct. You've cleared my mind.
    Thank you！

    Best regards,
    Hyodo