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SN65LVDT2: Expected failure mode for the receiver

Randhir Kalsi
Expert 4545 points
Part Number: SN65LVDT2

Hello team,

Hope you are well. Can you provide some feedback

recently discovered a design defect that results in a RS485 signal being fed to a LVDS receiver.  The receiver part number is SN65LVDT2DBVR.  Looking at the datasheet, the absolute maximum rating for the LVDS input is 4.0 V.  In theory we could be driving as high as 5V and in practice we are likely driving at around 4.5V

 

Our challenge is that we've already fielded systems with this defect and we are trying to assess the magnitude of our risk of field failures.  What is the expected failure mode for the receiver when operated under these conditions?

Regards,
Randhir

  • 0
    TI__Intellectual 2915 points
    Hi Randhir,

    We have received your question and will send you an update soon.

    Dennis
  • 0 in reply to Dennis Wu
    TI__Expert 4545 points
    Thanks Dennis. Any update?
  • 0
    TI__Intellectual 1810 points
    Hi Randhir,

    Sorry for this delayed response.

    SN65LVDT2 device certainly cannot handle RS485 signal levels! There are so many things that can go wrong and damage the SN65LVDT2 device:

    - RS485 driver output voltage can be any where from -7V to +12V. That exceeds the max absolute input voltage limits of the SN65LVDT2 which are -0.5 to +4V. The recommended voltage range for pins A and B is 0V to VCC-0.8V. You'll have to make sure that the connected RS485 driver has an output voltage that doesn't exceed those voltage levels.

    - RS485 driver differential output voltage amplitude can vary from 200mV to 5V. The maximum differential input voltage (VID) amplitude that can be handled by SN65LVDT2 is 1V. You need to verifying that the VID limits are not exceeded.

    - RS485 expects a termination of around 54ohm while SN65LVDT2 offers a 100ohm termination. Signal integrity maybe compromised in that case.

    Best regards,

    Hassan.