TPA2012D2
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SLOS438C–DECEMBER 2004–REVISED MARCH 2007
Decoupling Capacitor (CS)
The TPA2012D2 is a high-performance Class-D audio amplifier that requires adequate power supply decoupling
to ensure the efficiency is high and total harmonic distortion (THD) is low. For higher frequency transients,
spikes, or digital hash on the line a good low equivalent-series-resistance (ESR) ceramic capacitor, typically 1
µF, placed as close as possible to the device PVDD lead works best. Placing this decoupling capacitor close to
the TPA2012D2 is important for the efficiency of the Class-D amplifier, because any resistance or inductance in
the trace between the device and the capacitor can cause a loss in efficiency. For filtering lower-frequency noise
signals, a 4.7 µF or greater capacitor placed near the audio power amplifier would also help, but it is not
required in most applications because of the high PSRR of this device.
Table 1. Gain Setting
INPUT IMPEDANCE
GAIN
(V/V)
GAIN
(dB)
G1
G0
(RI)
(kΩ)
0
0
1
1
0
1
0
1
2
4
6
28.1
17.3
9.8
12
18
24
8
16
5.2
Input Capacitors (CI)
The TPA2012D2 does not require input coupling capacitors if the design uses a differential source that is biased
from 0.5 V to VDD– 0.8 V. If the input signal is not biased within the recommended common-mode input range, if
high pass filtering is needed (see Figure 34), or if using a single-ended source (see Figure 35), input coupling
capacitors are required.
The input capacitors and input resistors form a high-pass filter with the corner frequency, fc, determined in
Equation 1.
1
f +
c
ǒ
Ǔ
I
2p R C
I
(1)
The value of the input capacitor is important to consider as it directly affects the bass (low frequency)
performance of the circuit. Speakers in wireless phones cannot usually respond well to low frequencies, so the
corner frequency can be set to block low frequencies in this application. Not using input capacitors can increase
output offset.
Equation 2 is used to solve for the input coupling capacitance.
1
C +
I
ǒ
cǓ
2p R f
I
(2)
If the corner frequency is within the audio band, the capacitors should have a tolerance of ±10% or better,
because any mismatch in capacitance causes an impedance mismatch at the corner frequency and below.
12
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