FILTER FREE OPERATION AND FERRITE BEAD FILTERS

Ferrite

ChipBead

Ferrite

ChipBead

1nF

1nF

OUTP

OUTN

TPA2017D2

A ferrite bead filter can often be used if the design is failing radiated emissions without an LC filter and the

frequency sensitive circuit is greater than 1 MHz. This filter functions well for circuits that just have to pass FCC

and CE because FCC and CE only test radiated emissions greater than 30 MHz. When choosing a ferrite bead,

choose one with high impedance at high frequencies, and low impedance at low frequencies. In addition, select a

ferrite bead with adequate current rating to prevent distortion of the output signal.

Use an LC output filter if there are low frequency (< 1 MHz) EMI sensitive circuits and/or there are long leads

from amplifier to speaker. Figure 21 shows typical ferrite bead and LC output filters.

Figure 21. Typical Ferrite Bead Filter (Chip bead example: TDK: MPZ1608S221A)

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