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DS25CP102: Termination resistors

Josef Warta
Expert 4310 points
Part Number: DS25CP102

Hello team,

only for clarification about output termination resistors on DS25CP102:

Typical termination resistors are on the receiver side. Is there a reason why termination resistors can be also used on transmitter side?

Many Thanks

Josef

  • 0
    TI__Mastermind 43795 points

    Hi Josef,

    The resistors shown in the output structure of the DS25CP102 are there to indicate that the output impedance is ~ 100 Ohms during operation.  The DS25CP102 output does expect to see a 100 Ohm differential termination at the receiver side of the connected channel as well.

    Some low speed differential signals like MLVDS are designed to be terminated at both ends of the interconnect when multiple devices are connected to the same net.  This is most common on the clock signal across a backplane application.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Prodigy 20 points

    Hi everybody,

    this question came up because of the information given in the datasheet of the device "DS25CP102" on the first page : 

    "Each differential input and output is internally terminated with a 100Ω resistor to lower device insertion and return losses, reduce component count and further minimize board space. "

    and on page 4 (LVDS OUTPUT DC SPECIFICATIONS)

    "ROUT Output Termination Resistor Between OUT+ and OUT- 100 Ω"

    My thought was :

    To get a differential output voltage of 350mV at the 100 Ohm termination resistor on the receiver side the output stage must provide a current source of 3.5mA.

    If the output stage is also equipped with a 100 Ohm resistor the output stage must provide a 7mA current source to get the differential voltage of 350mV at the 100 Ohm termination resistor at the receiver.

     

    I haven´t found any information regarding the output stage or the current source in the datasheet.

     

    Is the DS25CP102 equipped with a 100 Ohm termination resistor at the output stage?

    In this case, are the output stages equipped with a 7mA current source?

    If the DS25CP102 is equipped with this output termination resistor, what is the reason? What is the benefit?

     

    Many Thanks!

    Best regards

    Andreas

  • 0 in reply to Andreas Bohnert
    TI__Mastermind 43795 points

    Hi Andreas,

    The DS25CP102 uses a voltage mode output to accomodate the internal loading.

    The internal resistance is part of the output structure to improve the return loss of the output.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Prodigy 20 points

    Hi Lee,

    this was an open point in my latest project.

    Thank you for clarification.

    Best regards

    Andreas