Datasheet

MAX9788
14V
P-P
, Class G Ceramic Speaker Driver
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Detailed Description
The MAX9788 Class G power amplifier with inverting
charge pump is the latest in linear amplifier technology.
The Class G output stage offers improved performance
over a Class AB amplifier while increasing efficiency to
extend battery life. The integrated inverting charge
pump generates a negative supply capable of deliver-
ing greater than 700mA.
The Class G output stage and the inverting charge
pump allow the MAX9788 to deliver a 14V
P-P
voltage
swing, up to two times greater than a traditional single-
supply linear amplifier.
Class G Operation
The MAX9788 Class G amplifier is a linear amplifier that
operates within a low (V
CC
to GND) and high (V
CC
to
SV
SS
) supply range. Figure 1 illustrates the transition
from the low to high supply range. For small signals,
the device operates within the lower (V
CC
to GND) sup-
ply range. In this range, the operation of the device
is identical to a traditional single-supply Class AB
amplifier where:
I
LOAD
= I
N1
As the output signal increases so a wider supply is need-
ed, the device begins its transition to the higher supply
range (V
CC
to SV
SS
) for the large signals. To ensure a
seamless transition between the low and high supply
ranges, both of the lower transistors are on so that:
I
LOAD
= I
N1
+ I
N2
As the output signal continues to increase, the transi-
tion to the high supply is complete. The device then
operates in the higher supply range, where the opera-
tion of the device is identical to a traditional dual-sup-
ply Class AB amplifier where:
I
LOAD
= I
N2
During operation, the output common-mode voltage of
the MAX9788 adjusts dynamically as the device transi-
tions between supply ranges.
Utilizing a Class G output stage with an inverting
charge pump allows the MAX9788 to realize a 20V
P-P
output swing with a 5V supply.
ON
I
N1
I
N1
P
N1
N2
I
P
ON
OFF
Z
L
V
CC
SV
SS
LOW SUPPLY RANGE OPERATION
I
P
= I
N1
ON
I
N2
I
N2
P
N1
N2
I
P
ON
ON
Z
L
V
CC
BTL CLASS G SUPPLY TRANSITION
SV
SS
SUPPLY TRANSITION
I
P
= I
N1
+ I
N2
ON P
N1
N2
I
P
OFF
ON
Z
L
V
CC
SV
SS
HIGH SUPPLY RANGE OPERATION
I
P
= I
N2
Figure 1. Class G Supply Transition