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

4.1 Step 1 - Verify ESR Meets Oscillator Requirements

Locate the crystal ESR specification in the datasheet of the crystal manufacturer. Crystal datasheets can label this as ESR, max ESR, or series resistance. Look up the maximum allowable ESR from Table 3-1 using the target frequency and intended load capacitor values (CL1 = CL2 = 12pF or 24pF column).

Check: Crystal ESR ≤ Table 3-1 Maximum ESR.

If the crystal ESR exceeds the table value, do not proceed with this crystal. ESR cannot be corrected by any external component. Select a different crystal with lower ESR. For a 20MHz crystal with CL1 = CL2 = 12pF, the maximum ESR is 45Ω.

When CL1 > 24pF: Use the 24pF column of Table 3-1 as a conservative upper bound. This is valid because ESRmax increases with CL1 across the table; the 24pF column gives the least restrictive limit that can be read from the characterized data.

Note: ESR is temperature-dependent and typically increases at cold temperatures. Always verify ESR at the lowest operating temperature of the application, not just at 25℃. Request full temperature characterization from the crystal manufacturer if the datasheet only provides a room-temperature ESR value.