FILTER FREE OPERATION AND FERRITE BEAD FILTERS

1nF

Ferrite

ChipBead

OUTP

OUTN

1nF

Ferrite

ChipBead

OPERATION WITH DACs AND CODECs

BYPASSING THE BOOST CONVERTER

TPA2014D1

A ferrite bead filter is often 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 a 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 16 shows a typical ferrite bead output filters.

Figure 16. Typical Ferrite Chip Bead Filter

Suggested Chip Ferrite Bead

Load

Vendor

Part Number

Size

8

Ω

Murata

BLM18EG121SN1

0603

When using switching amplifiers with CODECs and DACs, there may be an increase in the output noise floor

from the audio amplifier. This occurs when mixing of the output frequencies of the CODEC/DAC with the

switching frequencies of the audio amplifier input stage. The noise increase is solved by placing a low-pass filter

between the CODEC/DAC and audio amplifier. This filters off the high frequencies that cause the problem and

allow proper performance.

The TPA2014D1 has a two pole low pass filter at the inputs. The cutoff frequency of the filter is set to

approximately 100kHz. The integrated low pass filter of the TPA2014D1 eliminates the need for additional

external filtering components. A properly designed additional low pass filter may be added without altering the

performance of the device.

Bypass the boost converter to drive the Class-D amplifier directly from the battery. Place a Shottky diode

reverse breakdown voltage of 10 V or greater, and a forward voltage as small as possible. See Figure 17 for an

example of a circuit designed to bypass the boost converter.

enabled (SDb

the recommended operating range when the boost converter is disabled (SDb

≤ 0.3V).

Place a logic high on SDb to place the TPA2014D1 in boost mode. Place a logic low on SDb to place the

TPA2014D1 in bypass mode.

16

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