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LMH0344: SDI LMH0344/LMH0395

Lei wang
Expert 1620 points
Part Number: LMH0344
Other Parts Discussed in Thread: LMH0346, LMH1983, LMH0356

HI Sir:

     The SDI about the difference between  LMH0344 bypass FPGA and conect LMH0346 to FPGA? For the input crystal oscillator or clock chip FPGA technology requirements?Precision is less than how many PPM?

  • 0
    TI__Guru* 93670 points

    Hi Lei,

    Crystal tolerance is about +/-50ppm.

    Please clarify you mean by your first question? You can connect LMH0344 directly to the FPGA input. Or you can connect LMH0344 to LMH0346 as well. Or you may want to AC couple LMH0346 output to the LMH0346 input. These are are all possible.

    Regards,,nasser

  • 0 in reply to Nasser Mohammadi
    Expert 1620 points

    HI nasser:

      3 Question.

    1.The inductance be  recommended 3.9nH   5.6nH  6.8nH  8.1nH. which is suitable or All is OK?

         1.

    2.The LMH1983 be used in free-Run mode.  The Pin40  VC_LPF is not needed. Do we need config it by Register?  Or The default reg set is also can  output Clock1 to Clock4.

    3. The clock of LMH0346/LMH0356 is need Clock synchronization with FPGA?

     

  • 0 in reply to Lei wang
    TI__Guru* 93670 points

    Hi Lei,

    1). This depends on your pcb layout. On our evaluation board we use 6.8nH. 

    2). I believe you should be able to use register to control DAC register that sets the VCO frequency(in free-run mode). 

    3). FPGA normally uses it's own Clock and Data Recovery (CDR) circuit to generate recovered clock. FPGA can also use the recovered clock generated by LMH0346 but typically FPGA just uses data only from the LMH0346/LMH0356 device.

    Regards,,nasser