STDA033 October   2026 MSPM0G3105-Q1 , MSPM0G3106-Q1 , MSPM0G3107-Q1 , MSPM0G3505-Q1 , MSPM0G3506-Q1 , MSPM0G3507-Q1 , MSPM0L1227-Q1 , MSPM0L1228-Q1 , MSPM0L2227-Q1 , MSPM0L2228-Q1 , MSPM33C321A

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1.     How Does an Electromagnetic Field Start in a Circuit?
    2.     Near-Field and Far-Field Electromagnetic Fields
  5. 2Common Sources of EMI in Electronic Designs
    1. 2.1 Resistors
      1. 2.1.1 Equivalent Series Inductance (ESL)
      2. 2.1.2 Shunt Capacitance
      3. 2.1.3 Parasitic Capacitance to Ground
    2. 2.2 Capacitors
      1. 2.2.1 Equivalent Series Resistance (ESR)
      2. 2.2.2 Equivalent Series Inductance (ESL)
      3. 2.2.3 Leakage Resistance
      4. 2.2.4 Dielectric Absorption (Soakage)
    3. 2.3 Inductors
      1. 2.3.1 Direct Current Resistance (DCR)
      2. 2.3.2 Parasitic Capacitance
      3. 2.3.3 Core Losses (Magnetic Parasitics)
    4. 2.4 Summary of Discrete Component EMI Considerations
    5. 2.5 Design Deficiencies
    6. 2.6 Sources Specific to MCUs
      1. 2.6.1 Clock Circuits and Oscillators
    7. 2.7 Other Common Sources
      1. 2.7.1 High-Speed Digital Buses
      2. 2.7.2 I/O Output Transitions
      3. 2.7.3 Floating Components
      4. 2.7.4 External Environmental Sources
  6. 3Mitigation Techniques to Minimize EMI and Optimize Board Performance
    1. 3.1 Power Supply Capacitor Selection and Placement
    2. 3.2 Capacitor Placement
    3. 3.3 Layer Stack-Up Optimization
      1. 3.3.1 Good Stack-Up Traits
      2. 3.3.2 Stitching and Shielding Optimization Techniques
    4. 3.4 Trace Routing
    5. 3.5 Passive Pi Filtering
    6. 3.6 Shielding, Grounding, and Cable Boundaries
    7. 3.7 Transient and ESD Current Paths
  7. 4EMC Verification and Troubleshooting
    1. 4.1 Emissions and Immunity as Port Problems
    2. 4.2 Pre-Compliance Measurement Toolkit
    3. 4.3 A Frequency-to-Structure Debug Method
    4. 4.4 Interpreting Common Spectral Signatures
    5. 4.5 Integrated Design Review Checklist
  8. 5Conclusion

2.7.4 External Environmental Sources

External Environmental Sources: External electromagnetic energy becomes a problem when it couples into a susceptible port and is converted into a functional disturbance. Motors and relays generate inductive transients; radio transmitters produce continuous RF fields; electrostatic discharge injects fast current; and trace-to-trace crosstalk couples energy locally. Susceptibility depends on bandwidth, nonlinear junctions that demodulate RF, protection paths, firmware recovery, and the physical route of the injected current.

  • Electromechanical Devices: High-current loads such as motors, pumps, and relays generate significant transient noise and magnetic field coupling.
  • Communication Transmitters: Nearby cellular phones, Wi-Fi routers, and radio stations (TV, HAM, and so forth) emit RF energy that can be picked up by unshielded MCU traces.
  • Crosstalk: Closely spaced PCB traces can interfere with each other through inductive or capacitive coupling, where one signal (the "aggressor") disrupts another (the "victim").
  • Natural Phenomena: Occasional but intense disturbances from lightning strikes, electrostatic discharge (ESD), or solar flares can overwhelm protection systems.
Table 2-2 Environmental EMI Troubleshooting
DisturbancePrimary Coupling PathTypical SymptomFirst Control
Motor or relay transientShared supply or ground; magnetic loopReset, ADC error, interface faultLocal suppression and separated current loops
Nearby RF transmitterCable or trace common mode; enclosure apertureDemodulated noise or intermittent upsetBoundary filtering, shielding, balanced routing
CrosstalkMutual capacitance and inductanceFalse edge, timing jitter, analog errorSpacing, reference continuity, reduced edge rate
ESD type eventDirect or capacitive injection; chassis currentLatch-up, reset, permanent damageShort protection path to boundary or chassis