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DS91C176: how many DS91C176 points can we use in one LVDS bus?

Yunjing Wang1
Expert 3440 points
Part Number: DS91C176

Dear team,

My customer is using our DS91C176 in LVDS bus, when they use five DS91C176  in a LVDS BUS, the waveform of V_AB at No.5 DS91C176 shows large rise time,  this may cause by the large CL introduced by multipoint.

So I wanna know how many DS91C176 points can we use in one LVDS bus? 

  • 0
    TI__Mastermind 43795 points

    Hi,

    LVDS buses are designed for point to point operation - one driver and one receiver.  Placing multiple devices on an LVDS bus will usually result in longer rise/fall times do to the added capacitance of the devices and the interconnect.  In many cases the longer rise time is not a problem as long as the speed is low. 

    There is generally a direct relationship between the maximum possible bus speed and the number of LVDS I/O on the bus.  Adding LVDS devices to a bus will reduce the maximum possible speed on the bus.

    MLVDS is similar to LVDS and is designed for multiple device interconnects.  These interconnects can have over a dozen MLVDS devices on a single bus.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    TI__Expert 3440 points

    Hi Lee,

    Thank you for your reply.

    What the specific number of device do you mean by 'over a dozen MLVDS devices on a single bus' ?


    MLVDS standard illustrated MLVDS bus support up to 32 MLVDS devices on a single bus. So can we add 32 devices that use DS91C176 as driver or receiver on a single bus ?

    Best regards

    Yunjing

  • 0 in reply to Yunjing Wang1
    TI__Expert 3440 points

    Hi Lee,

    We think that large rise time issue comes from not matched impedance. We want review their PCB layout and do some simulation about impedance matching state.But we don't have a license of PADs.

    Can you help review their PCB layout and do a simulation experiment to analysis the impedance matching state of their layout? I will send their PCB layout to your email.

    Thank you!

    Regards

    Yunjing

  • 0 in reply to Yunjing Wang1
    TI__Mastermind 43795 points

    Hi Yunjing,

    I will look at the PCB. 

    Yes up to 32 devices are possible, but it can be difficult to achieve due to impedance matching and datarate requirements.

    Regards,

    Lee