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CDCLVC1104 Design

Pablo Fonovich
Intellectual 765 points
Other Parts Discussed in Thread: CDCLVC1104, PCM3168

Hi:

I want to use de CDCLVC1104 as a buffer for the clock signals that 2 ADC will recive from the same source...

I've read the datasheet, and in the "application" section 10.2 it uses a 50-Ohm trace before the CPU clock... Is this valid for ADC? the adc im using is PCM3168.

And how can i achieve that 50-Ohm trace? should i make PCB traces long for that? cause that makes me waste space.

And what happens if my PCB trace has much less than 50 Ohm? is there a problem or the datasheet just states one example?

I've read it but i don't find much clear... Is the first time i use buffer for clock

Can someone send me a refference design of how using the CDCLVC1104 pleas?

  • 0
    TI__Genius 10320 points
    Hi Pablo,

    We recommend using a 50 ohm trace to best match the output impedance of the CDCLVC1104. Depending on the supply voltage of the device, Rs (series resistor for impedance matching) will vary as noted in the DS.

    If this being designed on a PCB, your tool should allow you to calculate and control trace impedance by varying the width and length while taking into account the PCB stackup. 50 ohm traces are common so your tool should not have any issue here. If the driver impedance and trace impedance largely mismatch, your system will be prone to signal integrity issues, such as ringing.

    Gabe
  • 0 in reply to Gabe Ayala
    Intellectual 765 points
    Thanks for your answer... I've found how to implement the 50 Ohm traces in kicad... but now i have another question...
    If instead of using an Oscillator to source the clock i want to use the outputs of a McASP of an am335x... can i use the same CDCLVCx buffer? i've read that am335x has LVCMOS I/O but i find nothing in the TRM... can i use it or it's mandatory to use an external LVCMOS oscillator?
    Can you answer here although this question was verified or should i post a new question?
    Thanks
  • 0 in reply to Pablo Fonovich
    TI__Genius 10320 points
    Hi Pablo,

    This shouldn't be a problem if the signals from the am335x meet the electrical specs of the CDCLVC1xx. Again, here the coupling would be dependent on the signaling from the am335x but in the case of LVCMOS, there is a section in the DS that comments on proper termination.
    Note that the outputs of the am335x may be noisier than that of a dedicated oscillator, so depending on the requirements of the end buffered devices, one solution may be better and more necessary than the other.

    Gabe