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LMX2594EVM: EXTERNAL F_OSC

Marta Bautista
Prodigy 20 points

Part Number: LMX2594EVM
Other Parts Discussed in Thread: LMX2594

I am using an external reference of 10 MHz. When I use TICs Pro sw I have no problem to get the proper signal (and the LD lock indicator is on), but when I want to program all the registers with the option "import hex file" I am not able to fix this value of f_osc to 10 MHz. I can change the N divider and fraction numerator and denominator, but the f_osc is still 100 MHz (I am copying the registers that appear when I set the f_osc value at 10 MHz but this registers only affect the fractional parameters). So, my question is, how can I set the local oscilator at 10 MHz through the registers?

  • 0
    TI__Mastermind 28590 points
    Hello Marta,

    Note that the f_osc itself doesn't get programmed into the part. Just the divider values and such in the register map. So by saving/restoring the raw register data in hex format, this is not captured.

    If you want to save your TICS Pro EVM state, use file save/load to save the complete state of the TICS Pro software as a .tcs file.

    73,
    Timothy
  • 0 in reply to Timothy T
    Prodigy 20 points

    Hello Timothy,

    ok, but if I want to control it by means of a microcontroller (without using the software TICS pro) is could not be possible to use an external reference? Or how I could do it? Because, as I have seen the LD lock is only locked if it knows the right value of the f_osc.

    Thanks!

  • 0 in reply to Marta Bautista
    TI__Mastermind 28031 points

    Marta,

    The register set is sufficient to program the device.

    There is no actual need for the Fosc frequency for the part.  The LMX2594 does not really know the input frequency, but rather just the ratios of various frequencies.  The TICSPro tool shows the Fosc frequency as a convenience to the user, but it is really not required to actually program the part.  For instance, if your input frequency is 10 MHz and the output frequency is 8000 MHz, then the part will make make Fout/Fosc  = 8000/10 = 800.   Now if instead that 10 MHz frequency was 11 MHz, the output frequency would be 8800 MHz;  the part would not know the difference, nor is it apparent from the register settings.

    Regards,

    Dean