OUTP

OUTN

OUTP

Speaker

Current

OUTP

OUTN

OUTP-OUTN

Speaker

Current

OUTP

OUTN

OUTP-OUTN

Speaker

Current

0V

0V

PVCC

NoOutput

PositiveOutput

NegativeOutput

0A

0A

0V

-PVCC

OUTP-OUTN

TPA3110D2

SLOS528E – JULY 2009 – REVISED NOVEMBER 2015

www.ti.com

9.3 Feature Description

9.3.1 TPA3110D2 Modulation Scheme

The TPA3110D2 uses a modulation scheme that allows operation without the classic LC reconstruction filter

when the amp is driving an inductive load. Each output is switching from 0 volts to the supply voltage. The OUTP

and OUTN are in phase with each other with no input so that there is little or no current in the speaker. The duty

cycle of OUTP is greater than 50% and OUTN is less than 50% for positive output voltages. The duty cycle of

OUTP is less than 50% and OUTN is greater than 50% for negative output voltages. The voltage across the load

in the load.

Figure 35. The TPA3110D2 Output Voltage And Current Waveforms Into An Inductive Load

9.3.1.1 Ferrite Bead Filter Considerations

Using the Advanced Emissions Suppression Technology in the TPA3110D2 amplifier it is possible to design a

high efficiency Class-D audio amplifier while minimizing interference to surrounding circuits. It is also possible to

accomplish this with only a low-cost ferrite bead filter. In this case it is necessary to carefully select the ferrite

bead used in the filter.

One important aspect of the ferrite bead selection is the type of material used in the ferrite bead. Not all ferrite

material is alike, so it is important to select a material that is effective in the 10 to 100 MHz range which is key to

the operation of the Class D amplifier. Many of the specifications regulating consumer electronics have

emissions limits as low as 30 MHz. It is important to use the ferrite bead filter to block radiation in the 30 MHz

and above range from appearing on the speaker wires and the power supply lines which are good antennas for

these signals. The impedance of the ferrite bead can be used along with a small capacitor with a value in the

range of 1000 pF to reduce the frequency spectrum of the signal to an acceptable level. For best performance,

the resonant frequency of the ferrite bead/ capacitor filter should be less than 10 MHz.

14

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