Rainbow Electronics MAX9730 - Manual (Page 7)

MAX9730
2.4W, Single-Supply, Class G Power Amplifier
_______________________________________________________________________________________ 7
ON
I N1 I N1
P
N1
N2
I P
ON
OFF
R
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
R
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
R
L
V
CC
SV
SS
HIGH SUPPLY RANGE OPERATION
I P = I N2
Detailed Description
The MAX9730 Class G power amplifier with inverting
charge pump is the latest in linear amplifier technolo-
gy. The Class G output stage offers the performance
of a Class AB amplifier while increasing efficiency to
extend battery life. The integrated inverting charge
pump generates a negative supply capable of deliver-
ing up to 500mA.
The Class G output stage and the inverting charge pump
allow the MAX9730 to deliver an output power that is up
to four times greater than a traditional single-supply linear
amplifier. This allows the MAX9730 to maintain 0.8W into
an 8Ω load as the battery rail collapses.
Class G Operation and Efficiency
The MAX9730 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 amplifi-
er where:
I LOAD = I N1
As the output signal increases, so a wider supply is
needed, the device begins its transition to the higher sup-
ply 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 MAX9730 adjusts dynamically as the device transi-
tions between supply ranges.
Figure 1. Class G Supply Transition