User's Manual Stereo Amplifier TPA3008D2
Table Of Contents
- FEATURES
- DESCRIPTION
- APPLICATIONS
- ABSOLUTE MAXIMUM RATINGS
- DISSIPATION RATING TABLE
- RECOMMENDED OPERATING CONDITIONS
- AVAILABLE OPTIONS
- DC ELECTRICAL CHARACTERISTICS
- AC ELECTRICAL CHARACTERISTICS
- TYPICAL CHARACTERISTICS
- APPLICATION INFORMATION
- CLASS-D OPERATION
- Traditional Class-D Modulation Scheme
- TPA3008D2 Modulation Scheme
- Efficiency: LC Filter Required With the Traditional Class-D Modulation Scheme
- Effects of Applying a Square Wave Into a Speaker
- When to Use an Output Filter for EMI Suppression
- Gain setting via GAIN0 and GAIN1 inputs
- INPUT RESISTANCE
- INPUT CAPACITOR, CI
- SHUTDOWN OPERATION
- USING LOW-ESR CAPACITORS
- SHORT-CIRCUIT PROTECTION AND AUTOMATIC RECOVERY FEATURE
- THERMAL PROTECTION
- PRINTED-CIRCUIT BOARD (PCB) LAYOUT
- BASIC MEASUREMENT SYSTEM
- DIFFERENTIAL INPUT AND BTL OUTPUT
- CLASS-D RC LOW-PASS FILTER

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0 V
−12 V
+12 V
Current
OUTP
OUTN
Differential
Voltage
Across
Load
0 V
−12 V
+12 V
Current
OUTP
OUTN
Differential
Voltage
Across
Load
Output = 0 V
Output > 0 V
Efficiency: LC Filter Required With the Traditional Class-D Modulation Scheme
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
APPLICATION INFORMATION (continued)
Figure 18. The TPA3008D2 Output Voltage and Current Waveforms Into an Inductive Load
The main reason that the traditional class-D amplifier needs an output filter is that the switching waveform results
in maximum current flow. This causes more loss in the load, which causes lower efficiency. The ripple current is
large for the traditional modulation scheme, because the ripple current is proportional to voltage multiplied by the
time at that voltage. The differential voltage swing is 2 x V
CC
, and the time at each voltage is half the period for
the traditional modulation scheme. An ideal LC filter is needed to store the ripple current from each half cycle for
the next half cycle, while any resistance causes power dissipation. The speaker is both resistive and reactive,
whereas an LC filter is almost purely reactive.
The TPA3008D2 modulation scheme has little loss in the load without a filter because the pulses are short and
the change in voltage is V
CC
instead of 2 x V
CC
. As the output power increases, the pulses widen, making the
ripple current larger. Ripple current could be filtered with an LC filter for increased efficiency, but for most
applications the filter is not needed.
An LC filter with a cutoff frequency less than the class-D switching frequency allows the switching current to flow
through the filter instead of the load. The filter has less resistance than the speaker, which results in less power
dissipation, therefore increasing efficiency.
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