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

1.1 Capacitor Only Connected at the Class-D Outputs

A large capacitance >1nF can be connected to the amplifier output directly. This connection is not recommended as the output impedance of the Class-D is of a very low order approximately 0.5Ω which does not offer significant filtering (Filter cutoff> 300MHz). Further, in TAS27xx generation of devices increasing the capacitance at the Class-D output has negligible impact edge rate. Also, any capacitor directly connected to the Class-D output can significant degrade device efficiency and cause very high switching currents which can cause the device to shut down or reliability issues. For these reasons in TAS27XX family of devices the recommendation is to not connect maximum 200pF capacitance directly at the Class-D output.