TPA4860

1-W MONO AUDIO POWER AMPLIFIER

SLOS164A – SEPTEMBER 1996 – REVISED MARCH 2000

21

POST OFFICE BOX 655303

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)

1

C

B

25 k

Ω

v

1

C

1

R

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

1

2

pR

The main disadvantage, from a performance standpoint, is that the load impedances are typically small, which

summarizes the frequency response characteristics of each configuration.

Table 2. Common Load Impedances vs Low Frequency Output Characteristics in SE Mode

RL

CC

LOWEST FREQUENCY

8

Ω

68

µF

293 Hz

32

Ω

68

µF

73 Hz

47,000

Ω

68

µF

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.

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 k

Ω to 10 kΩ are recommended for 5-V and 3.3-V operation.