TPA3111D1_10 Datasheet, PDF (15/28 Pages) Texas Instruments – 10-W FILTER-FREE MONO CLASS-D AUDIO POWER AMPLIFIER with SPEAKER GUARD™

TPA3111D1
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CLASS-D OPERATION
This section focuses on the class-D operation of the TPA3111D1.
SLOS618A – AUGUST 2009 – REVISED JULY 2010
TPA3111D1 Modulation Scheme
The TPA3111D1 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 0 V throughout most of the switching period, greatly reducing the switching current, which reduces any I²R
losses in the load.
OUTP
OUTN
Differential
Voltage
Across
Load
+12 V
0V
-12 V
Current
Output = 0 V
OUTP
OUTN
Differential
Voltage
Across
Load
+12 V
0V
-12 V
Output > 0 V
Current
Figure 18. The TPA3111D1 Output Voltage and Current Waveforms Into an Inductive Load
Ferrite Bead Filter Considerations
Using the Advanced Emissions Suppression Technology in the TPA3111D1 amplifier it is possible to design a
high efficiency Class-D audio amplifier while minimizing interference to surrounding circuits. it is also possible to
accomplishthis 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
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