• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 34 subscribers
  • Views 546 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DS90LV804 - maximum cable reach application data

Rob Dockendorff
Prodigy 30 points
Other Parts Discussed in Thread: DS90LV804, DS90LV004

Hi,

The DS90LV804 is designed to be used as a backplane or cable receiver/driver.  Is there any application or test data that describes the cable reach that is achievable using this device?

I will be driving AC-coupled LVDS over CAT5, and need to set my expectations for cable reach if I select this device.

Thanks,

Rob

  • 0
    TI__Expert 3175 points

    Hi Rob,

    CAT5 is not a good cable for high speed data transmission. The cable reach is dependenly on the speed, and the amount of crosstalk introduced into the diff pair. RJ45 connector is notoriously poor in crosstalk for high speed, especially your have one RX pair and one TX adjacent pair.

    Can you clarify the data rate, how many pairs you used in the CAT5, and if they are same direction or opposite direction. Our applications engineer will look into this case and provide a response.

    Regards,

    TK Chin

  • 0 in reply to T.K. Chin
    Prodigy 30 points

    Hi Chin,

    Our data rate is 100 Mbps.  I believe CAT5 is rated to 100MHz.  We will have a TX pair, a RX pair, and a master-generated reference clock.  The 4th pair is used for lower speed house keeping, and will not be active during normal use.

    I'd like to put DS90LV804 on either side of this link to drive/recieve.

    Thanks for your help,
    Rob

  • 0 in reply to Rob Dockendorff
    TI__Mastermind 43795 points

    Hi Rob,

    The CAT5 cable has a typical NEXT of ~ -32 dB at 100 MHz.  With faster edge rates, additional high frequency contect will have much higher levels.  This will limit the maximum extension possible.  The DS90LV804 has an output bandwidth of almost 1 GHz.

    LVDS is also limited to a small common mode voltage range (approximately 0 - 2.4V).  It can be easily exceeeded when two pieces of equipment share only a cable connection. 

    Will the data transmitted be encoded in any way to maintain DC balance?  If there is a DC balance with the data, it should be possible to AC couple the signals and break the DC connection from chassis to chassis.  Ethernet uses a transformer to perform this function.

    Typical CAT5 loss is around 22-24dB/100 meters at 100 MHz.

    Since the DS90LV804 does not have any input or output signal equalization, the overall distance will be further limited.  I would estimate about 25 meters would be possible at 100 Mbps, but there must be accomodations made to break the DC path between driver and receiver. 

    If longer distances are required, the DS90LV004 can be used with its output Pre-Emphasis function to extend the distance by 10-15 meters. 

    Lee

  • 0 in reply to Lee Sledjeski
    Prodigy 30 points

    Hi Lee,

    Yes, we will be encoding the data to DC balance.  Our required data rate is 50Mbps, but it will pad out to 100Mbps after encoding.  I'd rather AC couple with capacitors than use transformers, but this isn't a hard requirement.

    We hope to stretch 10m with this interface, so I'd be very happy with a 25m limit.

    Thank you for your help.

    Rob