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

Table 1. MAX9779 Maximum Gain Settings

GAIN2

0

0

1

1

GAIN1

0

1

0

1

SPEAKER-MODE GAIN (dB)

15

16.5

18

19.5

HEADPHONE-MODE GAIN (dB)

0

0

3

3

Headphone Amplifier

In conventional single-supply headphone amplifiers,

the output-coupling capacitor is a major contributor of

audible clicks and pops. Upon startup, the amplifier

charges the coupling capacitor to its bias voltage, typical-

ly half the supply. Likewise, during shutdown, the capaci-

tor is discharged to GND. A DC shift across the capacitor

results, which in turn appears as an audible transient at

the speaker. Since the MAX9779 does not require output-

coupling capacitors, no audible transient occurs.

Additionally, the MAX9779 features extensive click-and-

pop suppression that eliminates any audible transient

sources internal to the device. The Power-Up/Down

Waveform in the Typical Operating Characteristics

shows that there are minimal spectral components in the

audible range at the output upon startup and shutdown.

Applications Information

BTL Speaker Amplifiers

The MAX9779 features speaker amplifiers designed to

drive a load differentially, a configuration referred to as

bridge-tied load (BTL). The BTL configuration (Figure 6)

offers advantages over the single-ended configuration,

where one side of the load is connected to ground.

Driving the load differentially doubles the output volt-

age compared to a single-ended amplifier under similar

conditions. Thus, the device’s differential gain is twice

the closed-loop gain of the input amplifier. The effective

gain is given by:

AVD

=

2

×

RF

RIN

Substituting 2 x VOUT(P-P) into the following equation

yields four times the output power due to double the

output voltage:

VRMS = VOUT(P−P)

22

POUT

=

VRMS2

RL

+1

VOUT(P-P)

2 x VOUT(P-P)

-1

VOUT(P-P)

Figure 6. Bridge-Tied Load Configuration

Since the differential outputs are biased at midsupply,

there is no net DC voltage across the load. This elimi-

nates the need for DC-blocking capacitors required for

single-ended amplifiers. These capacitors can be large

and expensive, can consume board space, and can

degrade low-frequency performance.

Power Dissipation and Heatsinking

Under normal operating conditions, the MAX9779 can dis-

sipate a significant amount of power. The maximum power

dissipation for the TQFN package is given in the Absolute

Maximum Ratings under Continuous Power Dissipation,

or can be calculated by the following equation:

PDISSPKG(MAX)

=

TJ(MAX) −

θ JA

TA

where TJ(MAX) is +150°C, TA is the ambient tempera-

ture, and θJA is the reciprocal of the derating factor in

°C/W as specified in the Absolute Maximum Ratings

section. For example, θJA of the thin QFN package is

+42°C/W. For optimum power dissipation, the exposed

paddle of the package should be connected to the

ground plane (see the Layout and Grounding section).

______________________________________________________________________________________ 13

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