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LMX2572: RAMP GENARATION

SATHYA PRIYA
Prodigy 40 points
Part Number: LMX2572

Hi, 

Is there any detailed description manual to understand on how to produce automatic ramping in LMX2572? Also, what is the minimum and maximum ramp frequencies that can be generated? 

  • 0
    TI__Guru* 82240 points

    Hi Sathya,

    Please check the EVM user's guide, there is an example. 

    For linear ramp without calibration, the ramp range is very limited, maybe around or less than 100MHz.

    With calibration, the ramp range can be 3.2GHz to 6.4GHz with CHDIV=1.

  • 0 in reply to Noel Fung
    Prodigy 40 points

    Hi Noel, 

    Thank you for the clarification. Also, can you let me know on how to change the frequency step size while running in the automatic ramping mode?

  • 0 in reply to SATHYA PRIYA
    Prodigy 40 points

    Hi Noel,

    What I meant was - how to find/fix the sweeping rate using TICS pro for LMX2572 PLL in automatic ramping mode.  

  • 0 in reply to SATHYA PRIYA
    TI__Guru* 82240 points

    Hi Sathya,

    in auto-ramp mode, the frequency will increment once every phase-detector-cycle. For example, if fpd=50MHz, then the frequency will ramp once every 20ns. If you want to complete the ramp in 100µs (assume linear ramp is possible here), then there will be 5000 ramps. If the freq ramp range is 200MHz, then each ramp will increment 40kHz. 

    200MHz linear ramp may not be possible with LMX2572, so we need to insert VCO calibration during ramp. As a result, the actual ramp time is longer than 100µs.