TPA4860 Datasheet, PDF (21/25 Pages) Texas Instruments – 1-W MONO AUDIO POWER AMPLIFIER

TPA4860
1-W MONO AUDIO POWER AMPLIFIER
SLOS164A – SEPTEMBER 1996 – REVISED MARCH 2000
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:
ǒ Ǔ ǒ Ǔ ^{1 v 1 Ơ 1}
C_B 25 kΩ
C_I R_I ^R_L^C_C
(12)
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.
+ f_{c high}
1
2pR_LC_C
(13)
The main disadvantage, from a performance standpoint, is that the load impedances are typically small, which
drives the low-frequency corner higher. Large values of C_C are required to pass low frequencies into the load.
Consider the example where a C_C of 68 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
RL
8Ω
32 Ω
47,000 Ω
CC
68 µF
68 µF
68 µF
LOWEST FREQUENCY
293 Hz
73 Hz
0.05 Hz
As Table 2 indicates, most of the bass response is attenuated into 8-Ω loads while headphone response is
adequate and drive into line level inputs (a home stereo for example) is very good.
headphone sense circuitry, R_pu
The TPA4860 is commonly used in systems where there is an internal speaker and a jack for driving external
loads (i.e., headphones). In these applications, it is usually desirable to mute the internal speaker(s) when the
external load is in use. The headphone inputs (HP-1, HP-2) and headphone output (HP-SENSE) of the TPA4860
were specifically designed for this purpose. Many standard headphone jacks are available with an internal
single-pole single-throw (SPST) switch that makes or breaks a circuit when the headphone plug is inserted.
Asserting either or both HP-1 and/or HP-2 high mutes the output stage of the amplifier and causes HP-SENSE
to go high. In battery-powered applications where power conservation is critical HP-SENSE can be connected
to the shutdown input as shown in Figure 39. This places the amplifier in a very low current state for maximum
power savings. Pullup resistors in the range from 1 kΩ to 10 kΩ are recommended for 5-V and 3.3-V operation.
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