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SN65LVDM176: Driver AC coupling

na na78
Guru 16770 points
Part Number: SN65LVDM176
Other Parts Discussed in Thread: TDP142

Hi

I suppose to use SN65LVDM176 for AUX channel of Displayport.

Could you please see the following sheet?

e2e_0603.xlsx

1. Is it possible to use SN65LVDM176 in such a use?

2. I set R1=50, R2=50.  Is it acceptable values?

BestRegards

  • 0
    TI__Mastermind 35130 points

    Hi,

    Please note that with R1 = 50 and R2 = 50, VOD will be double that of what's in the datasheet as the device is expecting a 50-ohm load (1 100-ohm termination on the driver side and another 100-ohm termination at the receiver side). Additionally, if the output is to be AC coupled you should ensure that the data is DC balanced. Also, what's the purpose of R3 and R4 in your schematic?

    Regards,

    I.K. 

  • 0 in reply to Ikechukwu Anyiam
    Guru 16770 points

    Hi I.K.

     

    Thank you for your reply.

     

    I think R3 and R4 are just required with the sourcing side of Displayport.

    You can also see these resistors in your TDP142 datasheets. (Maybe it is normal connection)

     

    I'm considering to replacement from FIN1019.

    As you pointed out, SN65LVDM176 shows VOD tested with 50ohm load conditions.

    On the other hands, FIN1019 is tested with 100ohm.

     

    Should we need to change the value of R1 and R2 to achieve the same VOD spec with FIN1019?

    (R1=R2=25ohm?)

     

     

    BestRegards

  • 0 in reply to na na78
    TI__Mastermind 35130 points

    Hi,

    Oh right, R3 and R4 are for DP aux termination so that is fine. 

    It is fine to keep R1=R2 = 50ohm. If you are concerned with the increased output swing with a 50ohm differential load you can put a small series resistor (~22 - 30ohm) on A and B like below:

    Regards,

    I.K.

  • 0 in reply to Ikechukwu Anyiam
    Guru 16770 points

    Hi I.K.

    Sorry for late reply.

    I appreciate the information from you.

    BestRegards