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LMX2615-SP: Condition that require VCOCal

Part Number: LMX2615-SP

Hello team,

My customer has a question about VCOCal of LMX2615-SP (PLL IC).

【Contents of question】

  • What are the conditions that require VCOCal when changing the frequency with serial externally?

(When setting the frequency between ± 500kHz, they would like to use it without VCO Cal if possible.)

  • In addition, is the phase likely to jump when the frequency is changed?

(They want to change the frequency continuously.)

I'm looking forward for hearing from you.

Best Regards,

Ryotaro Fukui

  • Hi Fukui-san,

    Because there are more than one VCO in the chip, VCO calibration is required in order to pick the right VCO. See https://www.ti.com/lit/pdf/snaa336 for details.

    However, if the VCO frequency change is small, for example, ± 500kHz, without VCO calibration, the VCO may remain lock without losing performance.

    LMX2615-SP does not support frequency ramping, so if you want a frequency sweep, you have to do it manually. That is, change the PLL_N, PLL_NUM and other relevant registers continuously.