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LMX2615-SP: Frequency hopping

Gregory Duperon
Expert 7490 points
Part Number: LMX2615-SP

I have a customer interested using LMX2615-SP in a frequency agile application.

The output frequency range is 8250 to 10250 MHz in 5MHz steps.  The reference frequency will be 100MHz.

The questions are as follows:

  1. What is the total time from the beginning of loading of the registers to a specified output frequency (including vco calibration and any other “housekeeping” functions that are necessary) to within 5 degrees settle tolerance?  In other words, what would be the minimum time between any frequency jump?
  2. Are those frequencies in the range and spacing specified exact?  Would there be any frequency error?
  3. If one were to use a 10MHz reference, what would be the minimum slew rate necessary for proper operation?

Thanks.

  • 0
    TI__Genius 11900 points

    Hello Gregory,

    The VCO calibration time is dependent on a variety of factors such as what VCO you start your calibration in, what VCO core the output frequency falls under. You can refer to http://www.ti.com/lit/an/snaa336/snaa336.pdf to understand this better.

    The frequencies should be exact without any expected ppm error. You can refer to "7.3.5 N Divider and Fractional Circuitry" section of the datasheet to verify this with Equation 2.

    A poor slew rate on your input can cause a degradation on the phase noise. Please refer to "Figure 11. PLL Phase Noise Metrics vs. Fosc Slew Rate" for an example at 200MHz.

    Thanks,

    Vibhu