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LMK03318: LMK03318 one differntial output swing is larger than others and spec.

wang shu
Intellectual 280 points
Part Number: LMK03318
Other Parts Discussed in Thread: CDCI6214, CDCI6214EVM

Hi,

I am using the LMK03318 to generate several differential outputs. But the output7 peak to peak swing is always larger than other output. The swing is almost about 2V that is larger than the maximum 1.6V spec too. The configuration of these outputs in TICS Pro are same.

Below are the schematic I am using. I measured the clock before the ac-coupling capacitors. So if believe the output swing should be same, no matter what the load is used after the capacitors.

Output7:

output 0, 2, and 5. the waveform are similar, only upload one.

  • 0
    TI__Mastermind 18990 points

    Wang,

    Is the 100-Ohm termination present on the receiver? Are the traces controlled 50-Ohms? This looks like reflections on the clock signal, which can impact the peak to peak measurement. 

    Thanks,

    Kadeem

  • 0 in reply to Kadeem Samuel
    Intellectual 280 points

    Hi Kadeem,

    The receiver of the output7 is CDCI6214 FB_P/N input, no 100ohm termination. But there is no 100ohm termination need in CDCI6214 datasheet.

    I check the CDCI6214EVM guide, looks like both two inputs has a 100 ohm termincation, but hte REF_P/N use another ac-coupling capacitors pairs again, so i don't think it has 100ohm termination at the inputs.

    For other LMK03318 outputs, i am using below way in TI doc "SLAA840". So is it a better way for CDCI6214 inputs with only one 100ohm termination?

     

    Regards,

    Shu

  • 0 in reply to wang shu
    TI__Expert 4505 points

    Hello Shu,

    The Figure 4 you referenced is from the CDCI6214 datasheet and depicts a 100 ohm termination at the inputs.

    Additionally, the LMK03318 datasheet shows how to configure the output. Since the CDCI6214 has no internal 100 ohm termination, this must be included externally in your design.

    Thanks,

    Cris