Datasheet

TPA311
350-mW MONO AUDIO POWER AMPLIFIER
SLOS207C – JANUARY 1998 – REVISED MAY 2003
26
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
single-ended operation (continued)
The output coupling capacitor required in single-supply SE mode also places additional constraints on the
selection of other components in the amplifier circuit. The rules described earlier still hold with the addition of
the following relationship:
(12)
10
ǒ
C
B
250 kΩ
Ǔ
v
1
ǒ
R
F
) R
I
Ǔ
C
I
Ơ
1
R
L
C
C
As an example, consider a circuit where C
B
is 0.2.2 µF, C
I
is 0.47 µF, C
C
is 330 µF, R
F
is 50 kΩR
L
is 32 Ω, and
R
I
is 10 kΩ. Inserting these values into the equation 12 we get:
18.2 t 35.5 Ơ 94.7 which satisfies the rule.
output coupling capacitor, C
C
In the typical single-supply SE 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 13.
(13)
f
c(high pass)
+
1
2p R
L
C
C
–3 dB
f
c
The main disadvantage, from a performance standpoint, is that the typically small load impedances drive 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 µF is chosen and loads vary from 8 Ω,
32 Ω, to 47 kΩ. Table 2 summarizes the frequency response characteristics of each configuration.
Table 2. Common Load Impedances vs Low Frequency Output Characteristics in SE Mode
R
L
C
C
LOWEST FREQUENCY
8 Ω 330 µF
60 Hz
32 Ω 330 µF Ą15 Hz
47,000 Ω 330 µF
0.01 Hz
As Table 2 indicates an 8-Ω load is adequate, earphone response is good, and drive into line level inputs (a home
stereo for example) is exceptional.