SNAA421 November   2025 LMK05318B , LMK5B12204 , LMK5B33216 , LMK5B33414 , LMK5C33216A , LMK5C33414A

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Start Here: Using TICS Pro for Configuration and Readback
    1. 1.1 TICS Pro Status Page
    2. 1.2 TICS Pro Default Setting
  5. 2Debug Procedure: From Device Start-Up to Locked Output State
    1. 2.1 Is the APLL Reference Valid?
      1. 2.1.1 Check Status of APLL Reference
      2. 2.1.2 Debug APLL Reference
    2. 2.2 Is the APLL Locked?
      1. 2.2.1 Check Status of APLL Lock
      2. 2.2.2 Debug APLL Lock
    3. 2.3 Is the DPLL Reference Valid?
      1. 2.3.1 Check Status of DPLL Reference Validation
      2. 2.3.2 Debug DPLL Reference Validation
    4. 2.4 Is the DPLL Selecting a Reference?
      1. 2.4.1 Check Status of DPLL Reference Selection
      2. 2.4.2 Debug DPLL Reference Selection
    5. 2.5 Is the DPLL Frequency Locked?
      1. 2.5.1 Check Status of DPLL Frequency Lock
      2. 2.5.2 Debug DPLL Frequency Lock
    6. 2.6 Is the DPLL Phase Locked?
      1. 2.6.1 Check Status of DPLL Phase Lock
      2. 2.6.2 Debug DPLL Phase Lock
  6. 3Summary
  7. 4References

2.1 Is the APLL Reference Valid?

The APLL cannot lock without a valid APLL reference and the DPLL cannot lock without a locked APLL. Therefore, the best practice is to check the APLL reference input clock. The APLL reference is commonly sourced from an external XO, TCXO, or OCXO. However, the LMK device also supports casaded APLL operation, using one APLL output as the APLL reference of another APLL. Figure 2-1 provides an example cascaded scheme. APLLx is the upstream APLL (cascaded source) and the APLL reference is the XO input. APLLy is the downstream APLL (cascaded APLL) and the APLL reference is the cascaded source.

Throughout the application note, the term "XO input" refers to any external source used as the APLL reference and the term "cascaded source" refers to any internal APLL source used as the APLL reference.

Cascaded APLL Reference ExampleFigure 2-1 Cascaded APLL Reference Example

Proceed to Is the APLL Locked? if the APLL reference is considered valid but the APLL and DPLL are not locked. Otherwise, refer to Check Status of APLL Reference and Debug APLL Reference.