TPA3110D2_0911 Datasheet, PDF (21/33 Pages) Texas Instruments – 15-W FILTER-FREE STEREO CLASS-D AUDIO POWER AMPLIFIER with SPEAKERGUARD™

TPA3110D2
www.ti.com................................................................................................................................................. SLOS528A – JULY 2009 – REVISED SEPTEMBER 2009
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
sits at 0V throughout most of the switching period, reducing the switching current, which reduces any I²R losses
in the load.
OUTP
OUTN
OUTP-OUTN 0V
Speaker
Current
OUTP
OUTN
PVCC
OUTP-OUTN 0V
Speaker
Current _0A
No Output
Positive Output
OUTP
OUTN
Negative Output
OUTP-OUTN 0V
-PVCC
Speaker ^0A
Current
Figure 39. The TPA3110D2 Output Voltage and Current Waveforms Into an Inductive Load
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.
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