cients, such as tantalum or aluminum electrolytic.

Capacitors with high-voltage coefficients, such as

ceramics, may result in an increase distortion at low

frequencies.

Other considerations when designing the input filter

include the constraints of the overall system, the actual

frequency band of interest and click-and-pop suppres-

sion. Although high-fidelity audio calls for a flat gain

response between 20Hz and 20kHz, portable voice-

reproduction devices such as cellular phones and two-

way radios need only concentrate on the frequency

range of the spoken human voice (typically 300Hz to

3.5kHz). In addition, speakers used in portable devices

typically have a poor response below 150Hz. Taking

these two factors into consideration, the input filter may

not need to be designed for a 20Hz to 20kHz response,

saving both board space and cost due to the use of

smaller capacitors.

BIAS Capacitor

THD+N by reducing power-supply noise at the common-

mode bias node, and serves as the primary click-and-

internal 25k

Ω source, and controls the rate at which the

common-mode bias voltage rises at startup and falls

during shutdown. For optimum click-and-pop suppres-

C

CR

k

BIAS

IN IN

≥ ⎡

⎣⎢

⎤

⎦⎥

10

25

Ω

1.4W and 1W, Ultra-Small, Audio Power

Amplifiers with Shutdown

______________________________________________________________________________________

11

OUTPUT

POWER (W)

INTERNAL POWER

DISSIPATION (W)

EFFICIENCY (%)

0.25

0.55

31.4

0.50

0.63

44.4

0.75

0.63

54.4

1.00

0.59

62.8

1.25

0.53

70.2

1.40

0.48

74.3

6

OUT-

IN+

BIAS

AUDIO INPUT

3

2

CLICKLESS/

POPLESS

SHUTDOWN

CONTROL

GND

SHDN

8

OUT+ 5

7

1

MAX4364

MAX4365

50k

Ω

50k

Ω

10k

Ω

10k

Ω

IN-

4

Figure 2. High-Gain Configuration

Table 1. Efficiency in a 5V, 8Ω BTL System