SNAA449 June   2025 LMX2820

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Various Options in Instant Calibration
    1. 2.1 When Delay for Instant Calibration Needs to be Increased From 2.5μs to 5μs
    2. 2.2 Generating the Lookup Table for Instant Calibration With the VCO Doubler
    3. 2.3 Reading Back the Instant Calibration Lookup Table Through SPI
    4. 2.4 Writing the Lookup Table Through SPI
    5. 2.5 Dealing With Case When Phase Detector Frequency is Changed Without Re-generating the Lookup Table
  6. 3Summary
  7. 4References

2.1 When Delay for Instant Calibration Needs to be Increased From 2.5μs to 5μs

The LMX2820 data sheet suggests a minimum delay for instant calibration of 2.5μs. However, there are cases when this is not sufficient and that this delay needs to be increased to 5μs. This is when the voltage at the VbiasVCO pin changes significantly. This can happen when switching across VCO cores or when the amplitude calibration setting changes significantly. Register used for this is INSTCAL_DLY(R2<11:1>).