MAX9820 データシートの表示（PDF） - Maxim Integrated

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MAX9820

DirectDrive Headphone Amplifier with External Gain

Maxim Integrated 

DirectDrive Headphone Amplifier

with External Gain

VOUT

VDD

VDD/2

VDD

GND

CONVENTIONAL DRIVER OUTPUT WAVEFORMS

VOUT

VDD

RF IMMUNITY vs. FREQUENCY

0

-20

-40

-60

LEFT CHANNEL

-80

-100

RIGHT CHANNEL

-120

0.8

1.35

1.90

2.45

3.00

FREQUENCY (GHz)

GND

2VDD

-VDD

MAX9820 OUTPUT WAVEFORMS

Figure 1. Conventional Driver Output Waveform vs. MAX9820

Output Waveform

GND (Figure 1). With no DC component, there is no

need for the large DC-blocking capacitors. The

MAX9820 charge pump requires two small ceramic

capacitors, conserving board space, reducing cost,

and improving the frequency response of the head-

phone amplifier.

Charge Pump

The MAX9820 features a low-noise charge pump. The

500kHz (typ) charge pump switching frequency is well

beyond the audio range and does not interfere with

audio signals.

Figure 2. MAX9820 RF Susceptibility

Click-and-Pop Suppression

In conventional single-supply audio amplifiers, the out-

put-coupling capacitor contributes significantly to audi-

ble clicks and pops. Upon startup, the amplifier

charges the coupling capacitor to its bias voltage, typi-

cally half the supply. Likewise, on shutdown, the capac-

itor is discharged. This results in a DC shift across the

capacitor, which appears as an audible transient at the

speaker. Since DirectDrive biases the outputs at

ground, this problem does not arise. Additionally, the

MAX9820 features extensive click-and-pop suppres-

sion that eliminates any audible transient sources inter-

nal to the device.

RF Susceptibility

Modern audio systems are often subject to RF radiation

from sources such as wireless and cellular phone net-

works. Although the RF radiation is out of the audio

band, many signals, GSM signals in particular, contain

bursts or modulation at audible frequencies. Most ana-

log amplifiers demodulate the low-frequency envelope,

adding noise to the audio signal. The MAX9820 archi-

tecture addresses the RF susceptibility problem by

rejecting RF noise and preventing it from coupling into

the audio band.

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