MAX9730EWP+TG45 Datasheet MAX9730EWP+TG45, MAX9730ETI+T | P7-P9

MAX9730

2.4W, Single-Supply, Class G Power Amplifier

_______________________________________________________________________________________ 7

OFF

LOW SUPPLY RANGE OPERATION

= I

BTL CLASS G SUPPLY TRANSITION

SUPPLY TRANSITION

= I

+ I

ON P

OFF

HIGH SUPPLY RANGE OPERATION

= I

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

to GND) and high (V

) supply range. Figure 1 illustrates the transition

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

the device operates within the lower (V

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:

LOAD

= I

As the output signal increases, so a wider supply is

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

ply range (V

to SV

) 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:

LOAD

= I

+ I

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:

LOAD

= I

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

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

) 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

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

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.

=×

⎛

⎝

⎜

⎞

⎠

⎟

⎡

⎣

⎢

⎤

⎦

⎥

()

20 4log

MAX9730

EFFICIENCY vs. CLASS AB

MAX9730 fig02

OUTPUT POWER (W)

EFFICIENCY (%)

1.51.00.5

100

0 2.0

MAX9730

TRADITIONAL CLASS AB

MAX9730

IN+

FB+

IN+

IN-

FB-

CLASS G

OUTPUT

STAGE

FB+

FB-

Figure 2. MAX9730 Efficiency vs. Class AB Efficiency vs.

Class D Efficiency

Figure 3. Gain Setting

MAX9730

2.4W, Single-Supply, Class G Power Amplifier

_______________________________________________________________________________________ 9

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

Component Selection

Input-Coupling Capacitor

The AC-coupling capacitors (C

IN_

) and input resistors

IN_

) form highpass filters that remove any DC bias from

an input signal (see the

Typical Application

Circuit/Functional Diagram

). C

IN_

blocks DC voltages

from the amplifier. The -3dB point of the highpass filter,

assuming zero source impedance due to the input signal

source, is given by:

Choose C

so that f

-3dB

is well below the lowest fre-

quency of interest. Setting f

-3dB

too high affects the

amplifier’s low frequency response. Use capacitors with

low-voltage coefficient dielectrics. Aluminum electrolytic,

tantalum, or film dielectric capacitors are good choices

for AC-coupling capacitors. Capacitors with high-voltage

coefficients, such as ceramics (non-C0G dielectrics),

can result in increased distortion at low frequencies.

Charge-Pump Capacitor Selection

Use capacitors with an ESR less than 50mΩ for opti-

mum performance. Low-ESR ceramic capacitors mini-

mize the output resistance of the charge pump. For

best performance over the extended temperature

range, select capacitors with an X7R dielectric.

Flying Capacitor (C1)

The value of the flying capacitor (C1) affects the load

regulation and output resistance of the charge pump. A

C1 value that is too small degrades the device’s ability

to provide sufficient current drive. Increasing the value

of C1 improves load regulation and reduces the charge-

pump output resistance to an extent. Above 1µF, the on-

resistance of the switches and the ESR of C1 and C2

dominate. A 4.7µF capacitor is recommended.

Hold Capacitor (C2)

The output capacitor value and ESR directly affect the

ripple at PV

. Increasing C2 reduces output ripple.

Likewise, decreasing the ESR of C2 reduces both rip-

ple and output resistance. A 10µF capacitor is recom-

mended.

Charge-Pump Frequency Set Resistor (R

)

The charge pump operates in two modes. When the

charge pump is loaded below 100mA, it operates in a

slow mode where the oscillation frequency is reduced

to 1/4 of its normal operating frequency. Once loaded,

the charge-pump oscillation frequency returns to nor-

mal operation. In applications where the design may be

sensitive to the operating charge-pump oscillation fre-

quency, the value of the external resistor R

can be

changed to adjust the charge-pump oscillation fre-

quency (see Figure 4).

IN IN

−

××

()

2π

IN IN+

−

CHARGE-PUMP OSCILLATION

FREQUENCY vs. R

MAX9730 fig04

(kΩ)

CHARGE-PUMP OSCILLATION FREQUENCY (kHz)

12510075

250

300

350

400

450

500

550

600

200

50 150

LOAD

> 100mA

Figure 4. Charge-Pump Oscillation Frequency vs. R

P1-P3 P4-P6 P7-P9 P10-P12

MAX9730EWP+TG45

Mfr. #:

Buy MAX9730EWP+TG45

Manufacturer:

Maxim Integrated

Description:

Audio Amplifiers 2.4W Class G Power Amplifier

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MAX9730EWP+TG45

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