MAX4411BEBE-T 查看數據表（PDF） - Maxim Integrated

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MAX4411BEBE-T

80mW, Fixed-Gain, DirectDrive, Stereo Headphone Amplifier with Shutdown

Maxim Integrated 

80mW, Fixed-Gain, DirectDrive, Stereo

Headphone Amplifier with Shutdown

MICROPHONE

AMPLIFIER

OUTPUT

AUDIO

INPUT

MICROPHONE

AMPLIFIER

MICROPHONE

BIAS

AUDIO

INPUT

MAX4411

HEADPHONE DRIVER

Figure 2. Earbud Speaker/Microphone Combination Headset

Configuration

method raises some issues:

• The sleeve is typically grounded to the chassis.

Using this biasing approach, the sleeve must be

isolated from system ground, complicating product

design.

• During an ESD strike, the driver’s ESD structures

are the only path to system ground. Thus, the driver

must be able to withstand the full ESD strike.

• When using the headphone jack as a line out to other

equipment, the bias voltage on the sleeve may con-

flict with the ground potential from other equipment,

resulting in possible damage to the drivers.

• When using a combination microphone and speaker

headset, the microphone typically requires a GND

reference. The driver DC bias on the sleeve conflicts

with the microphone requirements (Figure 2).

Low-Frequency Response

In addition to the cost and size disadvantages of the DC-

blocking capacitors required by conventional head-

phone amplifiers, these capacitors limit the amplifier’s

low-frequency response and can distort the audio signal:

1) The impedance of the headphone load and the DC-

blocking capacitor forms a highpass filter with the

-3dB point set by:

0

-3

-6

-9

-12

-15

-18

-21

-24

-27

-30

10

LOW-FREQUENCY ROLLOFF

(RL = 16Ω)

DirectDrive

330µF

220µF

100µF

33µF

100

1k

10k

100k

FREQUENCY (Hz)

Figure 3. Low-Frequency Attenuation for Common DC-Blocking

Capacitor Values

f−3dB

=

1

2πRLCOUT

where RL is the impedance of the headphone and

COUT is the value of the DC-blocking capacitor.

The highpass filter is required by conventional sin-

gle-ended, single power-supply headphone drivers

to block the midrail DC-bias component of the audio

signal from the headphones. The drawback to the

filter is that it can attenuate low-frequency signals.

Larger values of COUT reduce this effect but result

in physically larger, more expensive capacitors.

Figure 3 shows the relationship between the size of

COUT and the resulting low-frequency attenuation.

Note that the -3dB point for a 16Ω headphone with a

100µF blocking capacitor is 100Hz, well within the nor-

mal audio band, resulting in low-frequency attenuation

of the reproduced signal.

2) The voltage coefficient of the DC-blocking capacitor

contributes distortion to the reproduced audio signal

as the capacitance value varies as the function of

the voltage across the capacitor changes. At low

frequencies, the reactance of the capacitor domi-

nates at frequencies below the -3dB point and the

voltage coefficient appears as frequency-depen-

dent distortion. Figure 4 shows the THD+N intro-

10 ______________________________________________________________________________________

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