SWRA825 January   2025 IWR6843 , LP87745-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Regulatory Needs for Electro-Sensitive Protective Equipment (ESPE)
    2. 1.2 Different Types of Electro-Sensitive Protective Equipment (ESPE)
  5. 2Advantages of Radar Sensors in Industrial Applications
  6. 3Safety Concept Evaluation/Analysis
    1. 3.1 System Requirements
      1. 3.1.1 Stationary Use Case
      2. 3.1.2 Mobile Use Case
    2. 3.2 Considerations for Sensing Architectures
      1. 3.2.1 System Level Architecture
        1. 3.2.1.1 Bi-Static With Spatial Diversity
        2. 3.2.1.2 Co-Located Bi-Static (Two Sensor Products)
        3. 3.2.1.3 Co-Located Bi-Static (Single Sensor Product, Dual IWR6843)
        4. 3.2.1.4 Mono-Static (Single Sensor Product, Single IWR6843)
        5. 3.2.1.5 Summary
      2. 3.2.2 Latent Fault Monitoring
    3. 3.3 Sensor Level Architecture
      1. 3.3.1 Sensor Level Architecture for CAT 2
      2. 3.3.2 Sensor Level Architecture for Cat 3
  7. 4IEC TS 61496-5 Functional Test Results
  8. 5Other Considerations
    1. 5.1 Vibrations
    2. 5.2 Clock
  9. 6Conclusion
  10. 7References

5.2 Clock

The device-specific data sheet of the IWR6843 specifies that the crystal frequency tolerance should be ±50ppm and that those tolerances include initial frequency tolerance, drift over temperature aging and frequency pulling due to incorrect load capacitance.

In the case where a realistic failure of any of the above could lead to a drift of the crystal beyond the ±50ppm it should be noted that the only independent clock monitor in the IWR6843 is the RCOSC that only provides a few % of accuracy diagnostics. For more information, see the Monitoring and Diagnostic Mechanisms section in the IWR6843, IWR6443 Single-Chip 60- to 64-GHz mmWave Sensor Data Sheet. So an external monitor should be considered of which an option would be to output on pin N7 (MCU_CLK_OUT) with an output clock higher than 20MHz clock to avoid spurs in IF band (rather than OSC_CLKOUT on A14, as OSC_CLK_OUT only monitors the slicer output rather than the full clock tree. A simple MCU with a carefully selected additional crystal implementing a dual counter could help achieve this.