Texas Instruments TPA3003D2 - Manual (Page 29)

TPA3003D2
SLOS406A − FEBRUARY 2003 − REVISED MARCH 2003
29
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APPLICATION INFORMATION
Table 2. Recommended Minimum Wire Size for Power Cables
POUT
(W)
RL
( Ω )
AWG SIZE DC POWER LOSS
(mW)
AC POWER LOSS
(mW)
1 8 22 to 28 2.0 8.0 2.1 8.1
< 0.75 8 22 to 28 1.5 6.1 1.6 6.2
Class-D RC low-pass filter
A 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 31.
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.
R
FILT
R
L
R
FILT
C
FILT
V
L
= V
IN V
OUT
R
ANA
C
ANA
R
ANA
C
ANA
C
FILT
To APA
GND
AP Analyzer Input RC Low−Pass Filters Load
Figure 31. Measurement Low-Pass Filter Derivation Circuit—Class-D APAs