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MAX9730

2.4W, Single-Supply, Class G Power Amplifier

Maxim Integrated 

2.4W, Single-Supply, Class G Power Amplifier

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 (VCC to GND) and high (VCC to

SVSS) supply range. Figure 1 illustrates the transition

from the low to high supply range. For small signals,

the device operates within the lower (VCC 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:

ILOAD = IN1

As the output signal increases, so a wider supply is

needed, the device begins its transition to the higher sup-

ply range (VCC to SVSS) 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:

ILOAD = IN1 + IN2

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:

ILOAD = IN2

During operation, the output common-mode voltage of

the MAX9730 adjusts dynamically as the device transi-

tions between supply ranges.

BTL CLASS G SUPPLY TRANSITION

VCC

VCC

VCC

IP

ON

P

RL

IP

ON

P

RL

IP

ON P

RL

IN1

N1 ON

IN1

N1 ON

N1 OFF

N2 OFF

IN2

N2 ON

IN2

N2 ON

SVSS

LOW SUPPLY RANGE OPERATION

IP = IN1

SVSS

SUPPLY TRANSITION

IP = IN1 + IN2

SVSS

HIGH SUPPLY RANGE OPERATION

IP = IN2

Figure 1. Class G Supply Transition

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