TPA3123D2 Datasheet, PDF (12/29 Pages) Texas Instruments – 25-W STEREO CLASS-D AUDIO POWER AMPLIFIER

TPA3123D2
SLOS541A – JULY 2007 – REVISED AUGUST 2007
APPLICATION INFORMATION
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CLASS-D OPERATION
This section focuses on the class-D operation of the TPA3123D2.
Traditional Class-D Modulation Scheme
The TPA3123D2 operates in AD mode. There are two main configurations that may be used. For stereo
operation, the TPA3123D2 should be configured in a single-ended (SE) half-bridge amplifier. For mono
applications, TPA3123D2 may be used as a bridge-tied-load (BTL) amplifier. The traditional class-D modulation
scheme, which is used in the TPA3123D2 BTL configuration, 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
class-D modulation scheme with voltage and current waveforms is shown in Figure 23 and Figure 24.
+V_CC
0V
Output Current
Figure 23. Class-D Modulation for TPA3123D2 SE Configuration
+V_CC
0V
+V_CC
0V
+V_CC
Differential Voltage
Across Speaker
0V
–V_CC
Output Current
Figure 24. Class-D Modulation for TPA3123D2 BTL Configuration
Supply Pumping
One issue encountered in single ended (SE) class-D amplifier designs is supply pumping. Power-supply
pumping is a rise in the local supply voltage due to energy being driven back to the supply by operation of the
class-D amplifier. This phenomenon is most evident at low audio frequencies and when both channels are
operating at the same frequency and phase. At low levels, power supply pumping results in distortion in the
audio output due to fluctuations in supply voltage. At higher levels, pumping can cause the overvoltage
protection to operate, which temporarily shuts down the audio output.
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