• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 33 subscribers
  • Views 626 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

problem with DS90LV048ATMTC Differential Signal change with cable

jiulu gong
Prodigy 50 points
Other Parts Discussed in Thread: DS90LV048A

Hi, 

We got a problem with DS90LV048ATMTC.

 

The Differential Signal between VCLK-P and VCLK-N will change if we use different cables. And the max value will be 700mv and the min one is 500mv. Can anyone tell me the possible reasons? And what will happen, if we remove the pull-up resistor?

 

Thanks!

  • 0
    TI__Mastermind 43795 points

    Hi,

    Removing the resistor placed across the differential output pair will increase the VOD (output amplitude).  It is possible your cables have two different impedance values.  

    What is the resistor value?

    Were both cables connected to the same load on the other end?

    What is the resistor load value at the receive side?

    Regards,

    Lee 

  • 0 in reply to Lee Sledjeski
    Prodigy 50 points
    hi, Lee

    The value of pull-up resistor is 8.87k, and 5.1k for pull-down resistor.
    Yes, both cables connected to the same load on the other end.
    The resistor load value at the receive side is 100Omh

    Thanks,

    Jiulu
  • 0 in reply to jiulu gong
    TI__Mastermind 29655 points

    Hi Jiulu,

    The pull-up and pull-down resistor look like reasonable fail-safe biasing resistors, so I don't think you will see much difference when removing them.

    I believe Lee was referring to the characteristic impedance of the cables you are using. If the characteristic impedance of the cable is not 100-ohms, there may be some reflection effects due to the impedance mismatch between cable and your 100-ohm differential termination at the Rx end.

    1. Could you share the cable impedance for the cables you are using and which one is resulting in 500 or 700 mVpp?

    2. The minimum threshold for differential signaling is typically around -35 mV, so I do not believe that a difference between 500-700 mVpp will result in incorrect logic at the DS90LV048A output. Are you experiencing any issues at the DS90LV048A output?

    Thanks,

    Michael