Applications information – Rainbow Electronics MAX9730 User Manual
Page 8
MAX9730
2.4W, Single-Supply, Class G Power Amplifier
8
_______________________________________________________________________________________
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
the negative supply rail (PV
SS
) needed to create the
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)
shutdown mode. Connect SHDN to V
CC
for normal
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:
where A
V
is the desired voltage gain in dB. R
IN+
should
be equal to R
IN-
and R
FB+
should be equal to R
FB-
. The
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
MAX9730 fig02
OUTPUT POWER (W)
EFFICIENCY (%)
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+
R
IN+
R
IN-
C
IN-
C
IN-
IN-
FB-
-
CLASS G
OUTPUT
STAGE
R
FB+
R
FB-
Figure 2. MAX9730 Efficiency vs. Class AB Efficiency vs.
Class D Efficiency
Figure 3. Gain Setting