2.4W, Single-Supply, Class G Power Amplifier

8

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Utilizing a Class G output stage with an inverting

charge pump allows the MAX9730 to realize a 2.4W

output power with a 5V supply.

The theoretical best efficiency of a linear amplifier is

78%; however, that efficiency is only exhibited at peak

output powers. Under normal operating levels (typical

music reproduction levels), efficiency falls below 30%,

whereas the MAX9730 still exhibits 50% efficiency

under the same conditions.

Inverting Charge Pump

The MAX9730 features an integrated charge pump with

an inverted supply rail that can supply greater than

700mA over the positive 2.7V to 5.5V supply range. In

the case of the MAX9730, the charge pump generates

higher supply range, which allows the output of the

device to operate over a greater dynamic range as the

battery supply collapses over time.

Shutdown Mode

The MAX9730 has a shutdown mode that reduces

power consumption and extends battery life. Driving

SHDN low places the MAX9730 in a low-power (0.3µA)

operation.

Click-and-Pop Suppression

The MAX9730 Class G amplifier features Maxim’s com-

prehensive, industry-leading click-and-pop suppres-

sion. During startup, the click-and-pop suppression

circuitry eliminates any audible transient sources inter-

nal to the device.

Applications Information

Differential Input Amplifier

The MAX9730 features a differential input configuration,

making the device compatible with many CODECs, and

offering improved noise immunity over a single-ended

input amplifier. In devices such as PCs, noisy digital

signals can be picked up by the amplifier’s input

traces. The signals appear at the amplifiers’ inputs as

common-mode noise. A differential input amplifier

amplifies the difference of the two inputs, and signals

common to both inputs are canceled out. When config-

ured for differential inputs, the voltage gain of the

MAX9730 is set by:

Class G output stage has a fixed gain of 4V/V (12dB). Any

gain or attenuation set by the external input stage resistors

will add to or subtract from this fixed gain. See Figure 3.

A

R

R

dB

V

FB

IN

=×

⎛

⎝

⎜

⎞

⎠

⎟

⎡

⎣

⎢

⎢

⎤

⎦

⎥

20

4

log

_

_

MAX9730

EFFICIENCY vs. CLASS AB

OUTPUT POWER (W)

1.5

1.0

0.5

10

20

30

40

50

60

70

80

90

100

0

0

2.0

MAX9730

TRADITIONAL CLASS AB

MAX9730

+

IN+

FB+

IN-

FB-

-

CLASS G

OUTPUT

STAGE

Figure 2. MAX9730 Efficiency vs. Class AB Efficiency vs.

Class D Efficiency

Figure 3. Gain Setting