TPA2001D2
1-W FILTERLESS STEREO CLASS-D AUDIO POWER AMPLIFIER
SLOS292A – MARCH 2000 – REVISED APRIL 2000
APPLICATION INFORMATION
The value of C
i
is important as it directly affects the bass (low frequency) performance of the circuit. Consider
the example where Z
I
is 20 kΩ and the specification calls for a flat bass response down to 80 Hz. Equation 5
is reconfigured as equation 6.
C
i
+
1
2p Z
I
f
c
(6)
In this example, C
i
is 0.1
µF
so one would likely choose a value in the range of 0.1
µF
to 1
µF.
If the gain is known
and will be constant, use Z
I
from Table 1 to calculate C
i
. A further consideration for this capacitor is the leakage
path from the input source through the input network (C
i
) and the feedback network to the load. This leakage
current creates a dc offset voltage at the input to the amplifier that reduces useful headroom, especially in high
gain applications. For this reason a low-leakage tantalum or ceramic capacitor is the best choice. When
polarized capacitors are used, the positive side of the capacitor should face the amplifier input in most
applications as the dc level there is held at V
DD
/2, which is likely higher than the source dc level. Note that it
is important to confirm the capacitor polarity in the application.
C
i
must be 10 times smaller than the bypass capacitor to reduce clicking and popping noise from power on/off
and entering and leaving shutdown. After sizing C
i
for a given cut-off frequency, size the bypass capacitor to
10 times that of the input capacitor.
C
i
≤
C
BYP
/ 10
power supply decoupling, C
S
The TPA2001D2 is a high-performance CMOS audio amplifier that requires adequate power supply decoupling
to ensure the output total harmonic distortion (THD) is as low as possible. Power supply decoupling also
prevents oscillations for long lead lengths between the amplifier and the speaker. The optimum decoupling is
achieved by using two capacitors of different types that target different types of noise on the power supply leads.
For higher frequency transients, spikes, or digital hash on the line, a good low equivalent-series-resistance
(ESR) ceramic capacitor, typically 0.1
µF
placed as close as possible to the device V
DD
lead works best. For
filtering lower-frequency noise signals, a larger aluminum electrolytic capacitor of 10
µF
or greater placed near
the audio power amplifier is recommended.
midrail bypass capacitor, C
BYP
The midrail bypass capacitor, C
BYP
, is the most critical capacitor and serves several important functions. During
start-up or recovery from shutdown mode, C
BYP
determines the rate at which the amplifier starts up. The second
function is to reduce noise produced by the power supply caused by coupling into the output drive signal. This
noise is from the midrail generation circuit internal to the amplifier, which appears as degraded PSRR and
THD+N.
Bypass capacitor, C
BYP
, values of 0.47
µF
to 1
µF
ceramic or tantalum low-ESR capacitors are recommended
for the best THD and noise performance.
Increasing the bypass capacitor reduces clicking and popping noise from power on/off and entering and leaving
shutdown. To have minimal pop, C
BYP
should be 10 times larger than C
i
.
C
BYP
≥
10
×
C
i
(8)
(7)
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•
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9
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