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SN65HVD1781: SN65HVD1781 not working correctly at 3.3V ?

JUM
Prodigy 40 points
Part Number: SN65HVD1781

Connected a SN65HVD1781 (8 pin PDIP) to a UART Output of an STM32 Nucleo Evaluation board.
Added 120R Termination between A and B outputs, 1k pullup to Vcc and 1k pulldown to GND.
Part is working ok if powered by Vcc==5V, but has occasional bit errors looking like ground bouncing if powered by Vcc==3.31V.
Would like to show oscilloscope screen shots, but do not know how to attach. here?
Best regards, Juergen

  • 0
    Prodigy 40 points
    Sorry for inconveniences...
    Made this mistake: Connected #RE/DE to Nucleo µC pin PB3 - which is used by SWD trace.
    Reconnected to PB5 (unused GPIO) now SN65HVD1781 Driver is working ok with Vcc==3.3V too.
    Sorry!
  • 0 in reply to JUM
    TI__Intellectual 840 points

    Hi Juergen,

    I am reaching out to make sure everything is operating nominally?

    You should be able to drag and drop pictures in the text box during your original post and if not, you can click on the "Use rich formatting" button in the bottom right and in that you can drag and drop or use the dedicated insert media button. I hope that makes sense. 

    Regards,

    Daniel Noel

  • 0 in reply to Daniel R Noel
    Prodigy 40 points

    3.V issue solved (see above).


    Think found an error in data sheet on page 15. First line should read "VID > VIT+" ("greater than"):

  • 0 in reply to JUM
    TI__Intellectual 840 points

    Hi,

    I cannot find the line you are talking about on page 15 the closest one found was on page 17 and it read VIT+ < VID, in the current revision SLLS877H. You can see the revision at the top over every page next to the publication date. The previous revision should be SLLS877G.

    Regards,

    Daniel Noel

  • 0 in reply to Daniel R Noel
    Prodigy 40 points

    The document has resides here:

    www.ti.com/lit/gpn/sn65hvd1781-q1

    and has these title lines:

    SN65HVD178x-Q1 Fault-Protected RS-485 Transceivers With 3.3-V to 5-V Operation
    SLLSE49C –SEPTEMBER 2010–REVISED APRIL 2016

    On page 15 there is a table: "Table 3. Receiver Function Table" containing this line

    VID < VIT+ L H Receive valid bus High

    which I think should read

    VID > VIT+ L H Receive valid bus High

  • 0 in reply to JUM
    TI__Intellectual 840 points
    Hi,


    You are right I was looking at the non Q1 device. I will work on getting that fixed. Thank you for pointing that out.


    Regards,
    Daniel Noel