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I

)

I

1

C =

(2

f

R

c

´ p

´

´

(7)

FILTER FREE OPERATION AND FERRITE BEAD FILTERS

1nF

Ferrite

ChipBead

OUTP

OUTN

1nF

Ferrite

ChipBead

OPERATION WITH DACs AND CODECs

STEREO OPERATION APPLICATION

TPA2013D1

SLOS520 – AUGUST 2007

Any mismatch in capacitance between the two inputs inputs will cause a mismatch in the corner frequencies.

Choose capacitors with a tolerance of ±10% or better.

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 very 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 31 shows a typical ferrite bead output filters.

Figure 31. Typical Ferrite Chip Bead Filter

Suggested Chip Ferrite Bead

Load

Vendor

Part Number

Size

8

Ω

Murata

BLM18EG121SN1

0603

4

Ω

TDK

MPZ2012S101A

0805

When using switching amplifiers with CODECs and DACs, sometimes there is 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 can be 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 TPA2013D1 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 TPA2013D1 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.

Use the boost converter of the TPA2013D1 to supply the power for another audio amplifier when stereo

operation is required. Ensure the gains of the amplifiers match each other. This prevents one channel from

sounding louder than the other. Use Equation 1 through Equation 5 to determine R1, R2, boost inductor, and the

boost capacitor values. Figure 32 is an example schematic. The TPA2032D1 is a good choice for this

and the output power of the TPA2032D1 is on par with the TPA2013D1.

18

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