EMI Filter Component Recommendation

　　Ferrite bead filters for Class D amplifiers are derived empirically while measuring the radiated emissions.A ferrite bead should be rated for at least the peak load of the audio signal into the load impedance to prevent distortion of the class-D output signal. For example， if the Class D amplifier operates from 5 V intoa 4-Ω load， a ferrite bead with at least 1.5-A peak current capability should be selected. An impedancerating of 100 Ω or higher at high frequencies is recommended to ensure a high level of EMI suppression.

　　A capacitor that is not large in relation to the impedance of the ferrite bead is also needed to prevent largedrops in impedance at high frequencies. The value for these capacitors is often determined empirically，but 470 pF is a good starting point.

　　Figure 1 shows a recommended EMI Filter for AIC321x and AIC326x.