SDAA503 September   2026 F28E120SB , F28E120SC , F29H850DM , F29H850TU , F29H859TU-Q1 , F29P329SM-Q1 , F29P589DM-Q1 , F29P589DU-Q1 , TMS320F2800132 , TMS320F2800133 , TMS320F2800135 , TMS320F2800137 , TMS320F2800152-Q1 , TMS320F2800153-Q1 , TMS320F2800154-Q1 , TMS320F2800155 , TMS320F2800155-Q1 , TMS320F2800156-Q1 , TMS320F2800157 , TMS320F2800157-Q1 , TMS320F280021 , TMS320F280021-Q1 , TMS320F280023 , TMS320F280023-Q1 , TMS320F280023C , TMS320F280025 , TMS320F280025-Q1 , TMS320F280025C , TMS320F280025C-Q1 , TMS320F280033 , TMS320F280034 , TMS320F280034-Q1 , TMS320F280036-Q1 , TMS320F280036C-Q1 , TMS320F280037 , TMS320F280037-Q1 , TMS320F280037C , TMS320F280037C-Q1 , TMS320F280038-Q1 , TMS320F280038C-Q1 , TMS320F280039 , TMS320F280039-Q1 , TMS320F280039C , TMS320F280039C-Q1 , TMS320F280040-Q1 , TMS320F280040C-Q1 , TMS320F280041 , TMS320F280041-Q1 , TMS320F280041C , TMS320F280041C-Q1 , TMS320F280045 , TMS320F280048-Q1 , TMS320F280048C-Q1 , TMS320F280049 , TMS320F280049-Q1 , TMS320F280049C , TMS320F280049C-Q1 , TMS320F28075 , TMS320F28075-Q1 , TMS320F28076 , TMS320F28374D , TMS320F28374S , TMS320F28375D , TMS320F28375S , TMS320F28375S-Q1 , TMS320F28376D , TMS320F28376S , TMS320F28377D , TMS320F28377S , TMS320F28377S-Q1 , TMS320F28378D , TMS320F28378S , TMS320F28379D , TMS320F28379D-Q1 , TMS320F28379S , TMS320F28384D , TMS320F28384D-Q1 , TMS320F28384S , TMS320F28384S-Q1 , TMS320F28386D , TMS320F28386D-Q1 , TMS320F28386S , TMS320F28386S-Q1 , TMS320F28388D , TMS320F28388S , TMS320F28P550SG , TMS320F28P550SJ , TMS320F28P551SG , TMS320F28P559SG-Q1 , TMS320F28P559SJ-Q1 , TMS320F28P650DH , TMS320F28P650DK , TMS320F28P650SH , TMS320F28P650SK , TMS320F28P659DH-Q1 , TMS320F28P659DK-Q1 , TMS320F28P659SH-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Introduction
  5. 2 Pierce Oscillator and Crystal Model
    1. 2.1 Oscillator Block Diagram
    2. 2.2 Quartz Crystal Electrical Model
  6. 3 Crystal Selection Criteria
    1. 3.1 Why ESR Governs Crystal Compatibility
    2. 3.2 Crystal Frequency
    3. 3.3 Shunt Capacitance C0
  7. 4 Step-by-step Crystal Selection Process
    1. 4.1 Step 1 - Verify ESR Meets Oscillator Requirements
    2. 4.2 Step 2 - Size Load Capacitors CL1 and CL2
    3. 4.3 Step 3 - Determine if Damping Resistor Rd is Required
    4. 4.4 Step 4 - Calculate Rd (Damping Resistor)
    5. 4.5 Step 5 - Verify Negative Resistance (Rneg) Margin
  8. 5 PCB Layout Recommendations
    1. 5.1 Crystal Placement
    2. 5.2 Load Capacitor Placement
    3. 5.3 Trace Routing
    4. 5.4 Shielding Considerations
  9. 6 Testing and Validation
    1. 6.1 Measurement Equipment Requirements
    2. 6.2 Frequency Verification
    3. 6.3 Start-Up Time Measurement
    4. 6.4 Negative Resistance (Rneg) Measurement
  10. 7 Common Issues and Debug Tips
  11. 8 Design Example - 20MHz Crystal
  12. 9 Appendix A
    1. 9.1 Crystal Selection for Generic Pierce Oscillators
      1. 9.1.1 Introduction and Scope
      2. 9.1.2 Theoretical Background
      3. 9.1.3 Method A - Analytical Derivation from gm_min
        1. 9.1.3.1 Equipment and Component Requirements
        2. 9.1.3.2 Procedure
        3. 9.1.3.3 Single-Frequency Oscillator Considerations
        4. 9.1.3.4 Worked Example — 40MHz Fixed-Frequency Oscillator
      4. 9.1.4 Method B - Empirical Derivation using Negative Resistance Test
        1. 9.1.4.1 Equipment and Component Requirements
        2. 9.1.4.2 Signal Generator as Crystal Substitute
        3. 9.1.4.3 Equations
        4. 9.1.4.4 Procedure
        5. 9.1.4.5 Alternative Experimental Methods for Deriving gm
          1. 9.1.4.5.1 Load Capacitance (CL) Sweep
          2. 9.1.4.5.2 Supply Voltage (VDD) Sweep
          3. 9.1.4.5.3 Temperature Sweep (Thermal Margin Identification)
        6. 9.1.4.6 Generating a Custom ESR/CL Requirement Table
      5. 9.1.5 Method C - Frequency Pulling Characterization
        1. 9.1.5.1 Required Equipment and Components
        2. 9.1.5.2 Equations
        3. 9.1.5.3 Procedure
        4. 9.1.5.4 Worked Example - 40MHz Frequency Pulling
      6. 9.1.6 Summary Checklist - Generic Pierce Oscillator Crystal Selection
  13. 10References

5.4 Shielding Considerations

  • In high-noise environments (automotive, motor control), consider adding a conductive guard ring connected to ground around the crystal and its load capacitors. Some PCB manufacturers can also provide a ground-fill moat that physically isolates the crystal area from the rest of the board.
  • In EMI-sensitive applications, a metal crystal can with PCB mounting tabs connected to ground provides additional RF shielding.
Note: Many crystal manufacturers publish PCB layout recommendations specific to their packages (for example, 3225, 2520, 2016 form factors). These guidelines must be followed in addition to the previous device-level guidance.