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

3.1 Power Supply Capacitor Selection and Placement

Power integrity and EMI are the same problem viewed from different instruments. A power rail that bounces at high frequency forces return current through unexpected paths and can modulate I/O thresholds, ADC references, oscillator edges, and cable shields. Decoupling is the local energy path that keeps transient current from spreading across the board.

One way to mitigate or greatly reduce the emissions that are a result of this digital signal ringing is to analyze the capacitors attached to the VDD line to see the impedance characteristics over frequency. The frequency here is the key word. Design deficiencies are typically easily resolvable and can be mitigate

When selecting capacitors (following device recommended values), one key parameter to consider is the ESR of the capacitor. As you can see from the impedance versus frequency plot below, the impedance has a low point where the impedance is the smallest over a given frequency, which is preferred since we want to minimize any voltage drop caused by a high impedance value. Select decoupling by mounted impedance across the disturbance band. ESR creates damping and sets minimum impedance; ESL sets the high-frequency limit. Package size, orientation, pad length, via count, and distance to the IC can matter as much as nominal capacitance.

  • Use device-recommended capacitance as the starting point, then evaluate impedance at frequencies implied by edge rate and measured ringing.
  • Do not assume a three-value capacitor stack is always superior. Check for anti-resonance peaks created by the combined network.
  • Account for DC-bias derating, temperature, tolerance, and dielectric aging when estimating effective capacitance.
MSPM0 MSPM33 10μF Supply Capacitor ESR Impedance Over FrequencyFigure 3-1 10μF Supply Capacitor ESR Impedance Over Frequency
MSPM0 MSPM33 0.1μF Supply Capacitor ESR Impedance Over FrequencyFigure 3-2 0.1μF Supply Capacitor ESR Impedance Over Frequency
Tip: A decoupling capacitor does not 'absorb noise' in isolation. The capacitor provides a short local current path. The EMC value of the decoupling capacitor depends on the complete loop from IC power pin, through the capacitor, and back to the IC ground pin.