MAX9750 查看數據表（PDF） - Maxim Integrated

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MAX9750

2.6W Stereo Audio Power Amplifiers and DirectDrive Headphone Amplifiers

Maxim Integrated 

2.6W Stereo Audio Power Amplifiers and

DirectDrive Headphone Amplifiers

+1

VOUT(P-P)

2 x VOUT(P-P)

-1

VOUT(P-P)

Figure 9. Bridge-Tied Load Configuration

Applications Information

BTL Speaker Amplifiers

The MAX9750/MAX9751/MAX9755 feature speaker

amplifiers designed to drive a load differentially, a con-

figuration referred to as bridge-tied load (BTL). The BTL

configuration (Figure 9) offers advantages over the sin-

gle-ended configuration, where one side of the load is

connected to ground. Driving the load differentially

doubles the output voltage 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

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.

1000

VDD = 5V

100

RL = 16Ω

AV = 3dB

10

OUTPUTS IN PHASE

1

0.1

0.01

OUTPUTS 180° OUT OF PHASE

0.001

0

25 50 75 100 125 150

OUTPUT POWER (mW)

Figure 10. Total Harmonic Distortion Plus Noise vs. Output Power

with Inputs In/Out of Phase (Headphone Mode)

Power Dissipation and Heat Sinking

Under normal operating conditions, the MAX9750/

MAX9751/MAX9755 can dissipate a significant amount

of power. The maximum power dissipation for each

package is given in the Absolute Maximum Ratings

under Continuous Power Dissipation, or can be calcu-

lated 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).

For 8Ω applications, the worst-case power dissipation

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

in a power dissipation of about 1W. In this case, both the

TSSOP and TQFN packages can be used without violat-

ing the maximum power dissipation or exceeding the

thermal protection threshold. For 4Ω applications, the

TSSOP package may require heat-sinking or forced air

cooling to prevent the device from reaching its thermal

limit. The more thermally efficient TQFN package is sug-

gested 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

20 ______________________________________________________________________________________

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