
TPA0233
2W MONO AUDIO POWER AMPLIFIER
WITH HEADPHONE DRIVE
SLOS278D JANUARY 2000 REVISED NOVEMBER 2002
13
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
power supply decoupling, C(S)
The TPA0233 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
F placed as close as possible to the device VDD lead, works best. For
filtering lower-frequency noise signals, a larger aluminum electrolytic capacitor of 10
F 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-F to 1-F ceramic or tantalum low-ESR capacitors are
recommended for the best THD and noise performance.
output coupling capacitor, C(C)
In the typical single-supply stereo configuration, an output coupling capacitor (C(C)) is required to block the dc
bias at the output of the amplifier, thus preventing dc currents in the load. As with the input coupling capacitor,
the output coupling capacitor and impedance of the load form a high-pass filter governed by equation 6.
(6)
f
c(high) +
1
2
pR
L
C
(C)
3 dB
fc
The main disadvantage, from a performance standpoint, is the load impedances are typically small, which drives
the low-frequency corner higher, degrading the bass response. Large values of C(C) are required to pass low
frequencies into the load. Consider the example where a C(C) of 330 F is chosen and loads vary from 3 ,
4
, 8 , 32 , 10 k, to 47 k. Table 1 summarizes the frequency response characteristics of each
configuration.
Table 1. Common Load Impedances vs Low Frequency Output Characteristics in Stereo (SE) Mode
RL
C(C)
Lowest Frequency
3
330
F
161 Hz
4
330
F
120 Hz
8
330
F
60 Hz
32
330
F
15 Hz
10,000
330
F
0.05 Hz
47,000
330
F
0.01 Hz