TPA3107D2_07 Datasheet, PDF (14/36 Pages) Texas Instruments – 15-W STEREO CLASS-D AUDIO POWER AMPLIFIER

TPA3107D2
SLOS509A – OCTOBER 2006 – REVISED NOVEMBER 2006
APPLICATION INFORMATION (continued)
CLASS-D OPERATION
This section focuses on the class-D operation of the TPA3107D2.
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Traditional Class-D Modulation Scheme
The traditional class-D modulation scheme, which is used in the TPA032D0x family, has a differential output
where each output is 180 degrees out-of-phase and changes from ground to the supply voltage, V_CC. Therefore,
the differential prefiltered output varies between positive and negative V_CC, where filtered 50% duty cycle yields
0 V across the load. The traditional class-D modulation scheme with voltage and current waveforms is shown in
Figure 20. Note that even at an average of 0 V across the load (50% duty cycle), the current to the load is high,
causing high loss and thus causing a high supply current.
OUTP
OUTN
+12 V
Differential Voltage
Across Load ^{0 V}
-12 V
Current
Figure 20. Traditional Class-D Modulation Scheme's Output Voltage and Current Waveforms into an
Inductive Load With No Input
TPA3107D2 Modulation Scheme
The TPA3107D2 uses a modulation scheme that still has each output switching from 0 to the supply voltage.
However, OUTP and OUTN are now in phase with each other with no input. 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.
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