affects the low-frequency response of the system.

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

supply rejection ratio and THD+N by reducing power-

supply noise at the common-mode bias node, and

serves as the primary click-and-pop suppression

and controls the rate at which the common-mode bias

voltage rises at startup and falls during shutdown. For

optimum click-and-pop suppression, ensure that the

and-pop suppression is given by:

especially in single-ended applications.

Output-Coupling Capacitor

The MAX4366/MAX4367/MAX4368 require output-cou-

pling capacitors only when configured as a single-

ended amplifier. The output capacitor blocks the DC

component of the amplifier output, preventing DC cur-

rent flowing to the load. The output capacitor and the

load impedance form a highpass filter with the -3dB

point determined by:

As with the input capacitor, choose the output capacitor

frequency response of the system.

In addition to click-and-pop suppression and frequency

band considerations, the load impedance is another

vary, changing the -3dB point of the output filter. A

lower impedance increases the corner frequency,

adequate response.

Clickless/Popless Operation

achieves clickless/popless shutdown and startup. The

bias voltage rises on startup and falls when entering

shutdown. The size of the input capacitor also affects

to its quiescent DC voltage through the feedback resis-

transient at the amplifier’s output, which can result in an

effect, improving click-and-pop suppression.

Supply Bypassing

Proper supply bypassing ensures low-noise, low-distor-

tion performance. Place a 0.1µF ceramic capacitor in par-

bypass capacitors as close to the device as possible.

Headphone Applications

The MAX4366/MAX4368 can drive a mono headphone

when configured as a single-ended amplifier. Typical 2-

wire headphone plugs consist of a tip and sleeve. The tip

is the signal carrier while the sleeve is the ground con-

nection (Figure 5). Figure 6 shows the device configured

to drive headphones. OUT+ is connected to the tip,

delivering the signal to the headphone, while OUT-

remains unconnected.

f

RC

dB

L OUT

-3

1

2

=

π

C

CR

k

BIAS

IN IN

≤

Ω

⎡

⎣⎢

⎤

⎦⎥

10

25

330mW, Ultra-Small, Audio Power Amplifiers

with Shutdown

12

______________________________________________________________________________________

Figure 5. Typical 2-Wire Headphone Plug

TIP

(SIGNAL)

SLEEVE

(GND)