TPA3101D2_15 Datasheet, PDF (30/43 Pages) Texas Instruments – 10-W STEREO CLASS-D AUDIO POWER AMPLIFIER

TPA3101D2
SLOS473C – DECEMBER 2005 – REVISED SEPTEMBER 2007
Generator
V_GEN
R_GEN
R_GEN
Evaluation Module
Audio Power
Amplifier
C_IN
R_IN
C_IN
R_IN
R_OUT
R_L
R_OUT
Low-Pass
RC Filter
Low-Pass
RC Filter
Analyzer
R_ANA
R_ANA
C_ANA
C_ANA
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Twisted-Pair Wire
Twisted-Pair Wire
Figure 36. Differential Input, BTL Output Measurement Circuit
The generator should have balanced outputs, and the signal should be balanced for best results. An unbalanced
output can be used, but it may create a ground loop that affects the measurement accuracy. The analyzer must
also have balanced inputs for the system to be fully balanced, thereby cancelling out any common-mode noise in
the circuit and providing the most accurate measurement.
The following general rules should be followed when connecting to APAs with differential inputs and BTL outputs:
• Use a balanced source to supply the input signal.
• Use an analyzer with balanced inputs.
• Use twisted-pair wire for all connections.
• Use shielding when the system environment is noisy.
• Ensure that the cables from the power supply to the APA, and from the APA to the load, can handle the large
currents (see Table 3).
Table 3 shows the recommended wire size for the power supply and load cables of the APA system. The real
concern is the dc or ac power loss that occurs as the current flows through the cable. These recommendations
are based on 12-inch long wire with a 20-kHz sine-wave signal at 25°C.
Table 3. Recommended Minimum Wire Size for Power Cables
P_OUT (W)
10
2
1
< 0.75
R_L(Ω)
4
4
8
8
AWG Size
18
22
18
22
22
28
22
28
DC POWER LOSS
(MW)
16
40
3.2
8
2
8
1.5
6.1
AC POWER LOSS
(MW)
18
42
3.7
8.5
2.1
8.1
1.6
6.2
CLASS-D RC LOW-PASS FILTER
An RC filter is used to reduce the square-wave output when the analyzer inputs cannot process the pulse-width
modulated class-D output waveform. This filter has little effect on the measurement accuracy because the cutoff
frequency is set above the audio band. The high frequency of the square wave has negligible impact on
measurement accuracy because it is well above the audible frequency range, and the speaker cone cannot
respond at such a fast rate. The RC filter is not required when an LC low-pass filter is used, such as with the
class-D APAs that employ the traditional modulation scheme (TPA032D0x, TPA005Dxx).
The component values of the RC filter are selected using the equivalent output circuit as shown in Figure 37. R_L
is the load impedance that the APA is driving for the test. The analyzer input impedance specifications should be
available and substituted for R_ANA and C_ANA. The filter components, R_FILT and C_FILT, can then be derived for the
system. The filter should be grounded to the APA near the output ground pins or at the power supply ground pin
to minimize ground loops.
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