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LMX2491: frequency setting, variation and lock detect timing enquiry

Ernest Yong
Expert 4315 points
Part Number: LMX2491

Hi Team,

My customer are using two of such PLL  provided from a common clock, please see my enquiry below:

1. Will the O/p From the CHARGE PUMP will be identical for the same Frequency setting ?

2. What is the variation in CP Expected ?

3. Also does the Lock detect timing between the Two Pll are they the same across different PLL’s connected from the common clock ?

Best Regards,

Ernest

  • 0
    TI__Guru* 90900 points

    Hi Ernest,

    Both CP will turn ON at the same time as the trigger signal is coming from the shared reference clock (assuming the input path setting for both LMX parts are identical). However, the ON duration may differ as this duration is proportional to phase error between the input path and the feedback path (from the VCO). Furthermore, CP is a current source, there will be slight variation from part to part. 

    Lock detect response time may not necessary be exactly identical. There are counters in the DLD circuitry, for Pass and Error counting. Definitely these counters are not synchronized across parts, so we cannot assure all LD will response at the same time.