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.

RL is the load impedance that the APA is driving for the test. The analyzer input impedance specifications should

be available and substituted for RANA and CANA. The filter components, RFILT and CFILT, 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= VIN

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