MAX9779 查看數據表（PDF） - Maxim Integrated

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MAX9779

2.6W Stereo Audio Power Amplifier and DirectDrive Headphone Amplifier

Maxim Integrated 

2.6W Stereo Audio Power Amplifier and

DirectDrive Headphone Amplifier

1000

VDD = 5V

100

RL = 16Ω

AV = 3dB

10

OUTPUTS IN PHASE

1

0.1

0.01

0.001

0

OUTPUTS 180° OUT OF PHASE

25 50 75 100 125 150

OUTPUT POWER (mW)

Figure 7. Total Harmonic Distortion Plus Noise vs. Output Power

with Inputs In/Out of Phase (Headphone Mode)

For 8Ω applications, the worst-case power dissipation

occurs when the output power is 1.1W/channel, resulting

in a power dissipation of approximately 1W. In this case,

the TQFN package can be used without violating the

maximum power dissipation or exceeding the thermal

protection threshold. For 4Ω applications, the TQFN

package may require heatsinking or forced air cooling to

prevent the device from reaching its thermal limit. The

more thermally efficient TQFN package is suggested for

speaker loads less than 8Ω.

Output Power (Speaker Amplifier)

The increase in power delivered by the BTL configura-

tion directly results in an increase in internal power dis-

sipation over the single-ended configuration. The

maximum power dissipation for a given VDD and load is

given by the following equation:

PDISS(MAX)

=

2VDD2

π2RL

If the power dissipation for a given application exceeds

the maximum allowed for a given package, either reduce

VDD, increase load impedance, decrease the ambient

temperature, or add heatsinking to the device. Large

output, supply, and ground PC board traces improve the

maximum power dissipation in the package.

Thermal-overload protection limits total power dissipa-

tion in these devices. When the junction temperature

exceeds +160°C, the thermal-protection circuitry dis-

ables the amplifier output stage. The amplifiers are

enabled once the junction temperature cools by 15°C.

This results in a pulsing output under continuous ther-

mal-overload conditions as the device heats and cools.

Output Power (Headphone Amplifier)

The headphone amplifiers have been specified for the

worst-case scenario—when both inputs are in phase.

Under this condition, the drivers simultaneously draw

current from the charge pump, leading to a slight loss in

headroom of VSS. In typical stereo audio applications,

the left and right signals have differences in both magni-

tude and phase, subsequently leading to an increase in

the maximum attainable output power. Figure 7 shows

the two extreme cases for in and out of phase. In reality,

the available power lies between these extremes.

Power Supplies

The MAX9779 has different supplies for each portion of

the device, allowing for the optimum combination of

headroom, power dissipation, and noise immunity. The

speaker amplifiers are powered from PVDD. PVDD

ranges from 4.5V to 5.5V. The headphone amplifiers are

powered from HPVDD and VSS. HPVDD is the positive

supply of the headphone amplifiers and ranges from 3V

to 5.5V. VSS is the negative supply of the headphone

amplifiers. Connect VSS to CPVSS. The charge pump is

powered by CPVDD. CPVDD ranges from 3V to 5.5V and

should be the same potential as HPVDD. The charge

pump inverts the voltage at CPVDD, and the resulting

voltage appears at CPVSS. The remainder of the device

is powered by VDD.

Component Selection

Input Filtering

The input capacitor (CIN), in conjunction with the ampli-

fier input resistance (RIN), forms a highpass filter that

removes the DC bias from an incoming signal (see the

Block Diagram). The AC-coupling capacitor allows the

amplifier to bias the signal to an optimum DC level.

Assuming zero source impedance, the -3dB point of

the highpass filter is given by:

f−3dB

=

1

2πRINCIN

RIN is the amplifier’s internal input resistance value

given in the Electrical Characteristics. Choose CIN such

that f-3dB is well below the lowest frequency of interest.

Setting f-3dB too high affects the amplifier’s low-fre-

quency response. Use capacitors with low-voltage

coefficient dielectrics, such as tantalum or aluminum

electrolytic. Capacitors with high-voltage coefficients,

such as ceramics, may result in increased distortion at

low frequencies.

14 ______________________________________________________________________________________

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