Wireless-Phone Headset Application

Many wireless telephones feature an earbud speaker/in-

line microphone combination for hands-free use. One

common solution is to use a BTL amplifier that drives the

internal speaker and an earplug jack that mutes the inter-

nal speaker by physically disconnecting OUT- when a

headset is plugged in (Figure 7). The headset is driven

single-endedly, requiring an output-coupling capacitor,

Adding Volume Control

The addition of a digital potentiometer provides simple

volume control. Figure 8 shows the MAX4367/MAX4368

with the MAX5160 digital potentiometer used as an

input attenuator. Connect the high terminal of the

MAX5160 to the audio input, the low terminal to ground

tion passes the audio signal unattenuated. Setting the

wiper to the lowest position fully attenuates the input.

Use the 100k

Ω version of the MAX5160.

Layout Considerations

Good layout improves performance by decreasing the

amount of stray capacitance and noise at the amplifi-

er’s inputs and outputs. Decrease stray capacitance by

minimizing PC board trace lengths, using surface-

mount components and placing external components

as close to the device as possible.

UCSP Considerations

For general UCSP information and PC layout considera-

tions, please refer to the Maxim Application Note:

UCSP–A

Wafer-Level Chip-Scale Package.

330mW, Ultra-Small, Audio Power Amplifiers

with Shutdown

______________________________________________________________________________________

13

OUT+

HEADPHONE JACK

OUT-

8

5

C

OUT

MAX4366

MAX4367

MAX4368

Figure 6. MAX4367 Headphone Application Circuit

EARBUD SPEAKER

JACK

INTERNAL

LOUDSPEAKER

OUT+

OUT-

MAX4366

MAX4367

MAX4368

Figure 7. Headset with Internal Speaker Application Circuit

OUT+

AUDIO

INPUT

OUT-

IN-

3H

W5

4

5

8

C

IN

6L

MAX4367

MAX4368

MAX5160

Figure 8. MAX4367/MAX5160 Volume Control Circuit