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Original question:

LVDS or MLVDS

SN65LVDS1: Multi Drop driver : How to estimate the receivers node numbers drive by the SN65LVDS1

Julien MARIANNE7
Prodigy 20 points
Part Number: SN65LVDS1
Other Parts Discussed in Thread: SN65MLVD047A,

Hello,

I need to drive 6 LVDS recievers with only one driver in a multidrop topology, at 100MHz clock frequency.

I didn't find a single MLVDS driver ( there is 2 or 3 components with 4 channels or transceivers but no single driver) to realized the function.

My project is driven by saving space and power saving.

One of differences between LVDS driver and MLVDS driver is the output current .

On the MLVDS driver SN65MLVD047A datasheet,  the number of nodes is from 2 to 32 with a maximum output current of 24 mA. (FYI, package too large for my design)

In my case, I need only 6 nodes on one very short adapted differential trace, 10 cm maximum  between the source and the last recievers at a maximum frequency of 100MHz.

Q1 : Can I use the SN65LVDS1 (output current 10mA) single driver (or equivalents with 2 driver max) to drive 6 recievers with multidrop topology? 

Q2 : What is the formula or method to estimate the maximum current need to drive in function of nodes numbers, trace lenght and speed?

Thanks for your support.

Julien.

SN65MLVD047A

  • 0
    TI__Genius 10250 points
    Hello Julien,

    While an M-LVDS driver is more suitable for this, a regular LVDS driver can do multi-drop. I believe 6 nodes should be OK, but there is no formula per se. The biggest concern is not the current drive, rather the signal integrity, particularly the stubs from the 5 unterminated receivers and the reflections they cause. To minimize these issues, make sure the stubs are really short and pay extra attention to the characteristic impedance of the traces. Notice that M-LVDS drivers are slower and have controlled edge rates and that helps reduce reflections.

    Regards,
    Yaser
  • 0 in reply to Yaser Ibrahim
    Prodigy 20 points

    Hello Yaser,

    Thank you for your complete answer and now it is clearest for my design.

    Your explanations contributes to validate my hypotheses.

    Best Regards,

    Julien