SLOA339 July   2024 TAS2764 , TAS2764 , TAS2780 , TAS2780 , TAS2781 , TAS2781

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Capacitor Only Connected at the Class-D Outputs
    2. 1.2 LC Filter Connected at the Class-D Outputs
    3. 1.3 Ferrite Bead Filters
  5. 2EMI Filter Considerations
    1. 2.1 Impedance Consideration of EMI Filter
    2. 2.2 Device Reliability Constraint for High Output Voltage
    3. 2.3 EMI Filter Current Reliability
  6. 3Post Filter Feedback
  7. 4Loop Stability With Post Filter Feedback
  8. 5User Guide: EMI Filter Modeling and Post Filter Feedback Validation Tool
  9. 6Summary
  10. 7References

Impedance Consideration of EMI Filter

When using EMI filters, the inductor or bead and cap combination must be chosen appropriately to avoid extremely high currents due to resonance which can potentially trigger an the OCP (Over current protection) mechanism in the device. A simple guidance to avoid this is to use a filter with cutoff frequency (ω0) greater than 1.5MHz. This step is to avoid high currents due to resonance with audio, ultrasonic content as well as Class-D switching frequency energy at 384KHz and 768KHz. Further if resonance related over current shutdown is still observed even with higher cutoff frequencies. The recommendation is to increase the bead or inductor value and reduce the parallel capacitance to maintain same cutoff frequency.