Datasheet

+V
CC
0V
OutputCurrent
OutputCurrent
+V
CC
0V
+V
CC
0V
+V
CC
0V
–V
CC
DifferentialVoltage
AcrossSpeaker
TPA3121D2
SLOS537A –MAY 2008–REVISED AUGUST 2010 www.ti.com
APPLICATION INFORMATION
CLASS-D OPERATION
This section focuses on the class-D operation of the TPA3121D2.
Traditional Class-D Modulation Scheme
The TPA3121D2 operates in AD mode. There are two main configurations that may be used. For stereo
operation, the TPA3121D2 should be configured in a single-ended (SE) half-bridge amplifier. For mono
applications, TPA3121D2 may be used as a bridge-tied-load (BTL) amplifier. The traditional class-D modulation
scheme, which is used in the TPA3121D2 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 25
and Figure 26.
Figure 25. Class-D Modulation for TPA3121D2 SE Configuration
Figure 26. Class-D Modulation for TPA3121D2 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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