Class D Stereo Audio Power Amplifier Module User's Guide TPA005D12

TPA005D12 Class-D EVM Performance Characteristics
3-20
Details
3.6 TPA005D12 Class-D EVM Performance Characteristics
The TPA005D12 class-D stereo audio power amplifier EVM was tested using
an Audio Precision System II, model 2322, a 5-V regulated dc power supply,
and the TI PNP audio power amplifier evaluation platform set up as described
in Chapter 2. Results were obtained with 4-Ω and 8-Ω speaker loads. The
results are shown in Figures 3–11 through 3–17.
The frequency response shown in Figure 3–17 is a relatively flat 20 dB over
the 20 Hz to 100 kHz frequency range. The lower and upper frequency corners
can be adjusted to extend the frequency response.
Figure 3–11. Class-D Amplifier Frequency Response at 4 Ω
22.5
20
15
12.5
10
–5
17.5
10 100 1k
Voltage Amplification – dB
f – Frequency – Hz
VOLTAGE AMPLIFICATION
vs
FREQUENCY
10k 100k
7.5
5
0
–2.5
2.5
V
DD
= 5 V
R
L
= 4 Ω
TA = 25° C
Total harmonic distortion plus noise (THD+N) versus output power and
frequency is shown in Figures 3–12 through 3–15 below. Figures 3–12 and
3–13 show power sweeps at a fixed frequency of 1 kHz. Switching and input
noise begins to dominate at low power, while the distortion at the mid to upper
power levels is a function of the class-D amplifier and the inductor. The lower
frequency noise may be improved by either increasing the order of the filter or
by increasing the amplifier switching frequency, which will further attenuate the
switching noise in the audio band.
Midrange distortion is a combination of the switching noise of the output power
transistors in the IC and the magnetic field created by the inductors. This
distortion is minimized by good separation of the output filter inductors for each
channel and through good EMI-reduction layout techniques.