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LMX2820: LVPECL termination for OSCIN input

Matteo Ricci
Prodigy 240 points
Part Number: LMX2820
Other Parts Discussed in Thread: CDCLVP1102, LMK04610

Tool/software:

Hi team,

in the attached image there is the schematic for electrical connection between a 100 MHz LVPECL oscillator and the PLL LMX2820.

Between the 100 MHz oscillator and the PLL i inserted the buffer CDCLVP1102.

Is the attached diagram correct?

Best Regards,

Matteo Ricci

  • 0
    TI__Guru** 110530 points

    Hi  Matteo,

    Likely your oscillator needs shunt resistors, please check with oscillator datasheet.

    LMX2820 input requires AC-couple. 

  • 0 in reply to Noel Fung
    Prodigy 240 points

    Hi Noel,

    thank you for the answer.

    In the oscillator datasheet there isn't any information about the shunt resistor. I will try to contact the supplier.

    In the meantime, could you suggest some values for the shunt resistor?

    Ok for the AC-coupling at the PLL inputs. I will insert a 100 nF capacitor.

    The second output of the CDCLVP1102 is connected to the input of the LMK04610 (pins CLKIN0_P, CLKIN0_N). 

    Can i replicate the first output buffer?

    Thank you in advance.

    Best Regards,

    Matteo Ricci

  • +1 in reply to Matteo Ricci
    TI__Guru** 110530 points

    Hi Matteo,

    Typical shunt resistor for a LVPECL driver is 150Ω. 

    LMK04610 input also requires AC-couple, same schematic applies to LMK CLKin.