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LMX2571: LMX2571 fractional spurs

Part Number: LMX2571

Hi TI experts

     our customers use LMX2571 external VCO as PLL.  clock frequency: 19.2MHz, PFD frequency 19.2/4=4.8MHz. When the frequency  is 25/26/27/28 times of clock frequency_19.2MHz, the fractional spurs are  poor and the R47 register is set to Weak. what is the reason?

  • Hi Harry,

    All the said output frequencies are integer multiple of the reference clock, there will be no fractional spurs. What is the spurs frequency? What is the loop filter bandwidth? R47, DITHERING, is a configurable register, you should set it according to your application need.