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LMK00334-Q1: CLKout0 and CLKout0*

David Park
Expert 6610 points
Part Number: LMK00334-Q1

Hi,

There are a couple of questions.

Customer is using only CLKin0 and CLKin0*

1. At CLKin0: toggle, CLKin0*, CLKout0 is toggled signal and CLKout0* is Hi-Z. Is it correct?

2. page 16 of datasheet

Is LMK input in figure 9-2 CLKin0 and CLKin0* in question1?

3. Does trace need 50Ohm matching?

Thanks.

  • 0
    TI__Expert 8421 points

    David,

    I am little confused with your first question.  If you wish to use CLKIN0/0* as a single ended CMOS input, then yes you would configure it as in figure 9-2 of the datasheet.  The LMK00304-Q1 has HCSL outputs which are differential, so they need two outputs.  So if CLKout0 is enabled then both CLKout0 and CLKout0* will output a signal.  Finally, yes 50ohm impedance matching is recommended to reduce reflections.  The input trace may need a Resistor  (Rs) as shown in figure 9-2 of the datasheet, and its value will be dependent on the output driver impedance of whatever is driving your CLKin.

    Regards,

    Will

  • 0 in reply to William Pfennigwerth
    TI__Expert 6610 points

    Hi William,

    Please refer below signal and schematic.

    1. CLKout0: toggle, CLKout0*: high at Vcc*0.5 Is it correct?

    2. 50Ohm impedance after RC(4.7Ohm) Is it available?

    3. CLK1B and CLK2B is from DOUT of ISL55100A. Does CMOS driver have same type output as DOUT of ISL55100A?

    Thanks.

  • 0 in reply to David Park
    TI__Expert 8421 points

    David, 

    I will get back to you by the end of the week.

    Regards,

    Will

  • 0 in reply to William Pfennigwerth
    TI__Expert 8421 points

    David,

    I see now that you are trying to implement a DC-Coupled LVCMOS input from the datasheet.  

      

    1. The CLKIN will be set according to the Single-Ended input you are describing, with CLKin0 toggling and CLKin0* set at ((Vo, pp)/2) *.5.  But the output, CLKout0 and CLKout0* will both be toggling.  The outputs will also not be at the same voltage swing Voltage High or Low as the inputs.  The HCSL output drivers would have a swing around 810 mV with a common mode voltage of ~ 405 mV.  

    2. The 50ohm is coming from the trace impedance.

    3. The LMK00334-Q1 has 4 differential HCSL outputs and one LVCMOS output.  It seems like the ISL55100A can be configured in many single ended output formats, but you can configure it in LVCMOS.  

    Let me know if you have any further questions,

    Will