Datasheet

MAX9788
14V
P-P
, Class G Ceramic Speaker Driver
8 _______________________________________________________________________________________
Inverting Charge Pump
The MAX9788 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 MAX9788, 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 col-
lapses over time.
Shutdown Mode
The MAX9788 has a shutdown mode that reduces
power consumption and extends battery life. Driving
SHDN low places the MAX9788 in a low-power (0.3µA)
shutdown mode. Connect SHDN to V
CC
for normal
operation.
Click-and-Pop Suppression
The MAX9788 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 MAX9788 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 amplifier’s 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
MAX9788 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 2.
In differential input configurations, the common-mode
rejection ratio (CMRR) is primarily limited by the exter-
nal resistor and capacitor matching. Ideally, to achieve
the highest possible CMRR, the following external com-
ponents should be selected where:
and
CC
IN IN+
=
−
R
R
R
R
FB
IN
FB
IN
+
+
=
−
−
A
R
R
dB
V
FB
IN
=×
⎛
⎝
⎜
⎞
⎠
⎟
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
()
20 4log
_
_
MAX9788
+
IN+
FB+
R
IN+
R
IN-
C
IN+
C
IN-
IN-
FB-
-
CLASS G
OUTPUT
STAGE
R
FB+
R
FB-
Figure 2. Gain Setting