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CDCLVP1216: Delete pull-up and pull-down resistors

David Hu
Prodigy 90 points
Part Number: CDCLVP1216
Other Parts Discussed in Thread: CDCLVP1208, CDCLVP1212, LMK00301, LMK00334

Dear Sir,

We have a project which need clock buffer, here we choose TI solution cdclvp1216, we have ever a design which used cdclvp1208, and found that all the downstream clock channels they have pull-up resistor and pull-down resistor, I can't quite understand their application here, can we delete these resistors?

Regards,

David hu

Below is our reference design from another project:

Below is our design refer to the CDCLVP1208 solution:

Here I delete the pull-up resistor and pull-down resistors, whether it is OK?

  • 0 in reply to David Hu
    TI__Genius 9920 points
    Hi David,
    Pull up 73.2 kOhm to 3.3V, pull down 10 kOhm to ground. It set a new bias voltage around 0.4V after AC capacitors.
    If there is a bias at receiver side (after AC 100nF), you could delete external bias resistors.
    If you need a different bias than 0.4 V, you could tune the pull-up resistor and pull-down resistor.
    Make sure there is 100 Ohm equivalent load at receiver side.

    Regards,
    Shawn
  • 0 in reply to Shawn Han
    Prodigy 90 points

    Hi Shawn,

    Thanks for your feedback, we know  the inputs of CDCLVP1216 can be LVPECL, LVDS, or LVCMOS/LVTTL. so we need to tune the pull-up and pull-down resistors to tune the bias so they can meet the reciever side.

    Another questions is that my colleague think this part can not support long length on PCB routing. Here we use the CDCLVP1216 as PCIe clock differencial pair to differents SSDs. and the routh length will be at least 18inch.

    So my colleague suggest IDT Parts 9DBV0941-AKILF to me, which specially used for PCIe clock line.

    my questions is whether CDCLVP1216(or CDCLVP1212) can support long length PCIe clock pair， if not, would you have proper part to suggest; if yes,how about the bias I set here?

    Regards,

    David Hu

  • 0 in reply to David Hu
    TI__Genius 9920 points
    Hi David,
    18 inch is no problem for LVPECL driver (CDCLVP1216).
    But for PCIe clock, it is HCSL type. I'll recommend LMK00301.

    Regards,
    Shawn
  • 0 in reply to Shawn Han
    Prodigy 90 points

    Hi Shawn,

    Thanks very much for your recommendation LMK00301,

    Here I still has a question is that I have ever used your clock buffer LMK00334 on our another project, and the circuit as below. Unfortunately we found there are no clock output on the nets CLKOUTA0P/N and CLKOUTA1P/N.

    Any issues had on this circuit, would you kindly help to point out?  tks!

    Regards,

    David Hu

  • 0 in reply to David Hu
    TI__Genius 9920 points

    Hi David,

    Please input it into a new post. It is better to have each thread to solve an individual issue. 

    Send me a remind email, I could response to you than other application engineers.

    I estimated it is an problem from HCSL DC bias 50 Ohm, I didn't see 50 Ohm to GND for HCSL driver.

    I'll close this post in case other E2E user confused.

    Thanks!

    Regards,

    Shawn