MAX4411BEBE-T 查看數據表（PDF） - Maxim Integrated

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MAX4411BEBE-T

80mW, Fixed-Gain, DirectDrive, Stereo Headphone Amplifier with Shutdown

Maxim Integrated 

80mW, Fixed-Gain, DirectDrive, Stereo

Headphone Amplifier with Shutdown

ADDITIONAL THD+N DUE

TO DC-BLOCKING CAPACITORS

10

1

0.1

TANTALUM

0.01

0.001

ALUM/ELEC

0.0001

10

100

1k

10k

100k

FREQUENCY (Hz)

Figure 4. Distortion Contributed by DC-Blocking Capacitors

duced by two different capacitor dielectric types.

Note that below 100Hz, THD+N increases rapidly.

The combination of low-frequency attenuation and fre-

quency-dependent distortion compromises audio repro-

duction in portable audio equipment that emphasizes

low-frequency effects such as multimedia laptops, as

well as MP3, CD, and DVD players. By eliminating the

DC-blocking capacitors through DirectDrive technology,

these capacitor-related deficiencies are eliminated.

Charge Pump

The MAX4411 features a low-noise charge pump. The

320kHz switching frequency is well beyond the audio

range, and thus does not interfere with the audio sig-

nals. The switch drivers feature a controlled switching

speed that minimizes noise generated by turn-on and

turn-off transients. By limiting the switching speed of the

charge pump, the di/dt noise caused by the parasitic

bond wire and trace inductance is minimized. Although

not typically required, additional high-frequency noise

attenuation can be achieved by increasing the size of

C2 (see Typical Application Circuit).

Shutdown

The MAX4411 features two shutdown controls allowing

either channel to be shut down or muted independently.

SHDNL controls the left channel while SHDNR controls

the right channel. Driving either SHDN_ low disables

the respective channel, sets the driver output imped-

ance to 1kΩ, and reduces the supply current. When

both SHDN_ inputs are driven low, the charge pump is

also disabled, further reducing supply current draw to

6µA. The charge pump is enabled once either SHDN_

input is driven high.

Click-and-Pop Suppression

In conventional single-supply audio drivers, the output-

coupling capacitor is a major contributor of audible

clicks and pops. Upon startup, the driver charges the

coupling capacitor to its bias voltage, typically half the

supply. Likewise, on shutdown, the capacitor is dis-

charged to GND. This results in a DC shift across the

capacitor, which in turn, appears as an audible transient

at the speaker. Since the MAX4411 does not require

output-coupling capacitors, this does not arise.

Additionally, the MAX4411 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 or shutdown.

In most applications, the output of the preamplifier dri-

ving the MAX4411 has a DC bias of typically half the

supply. At startup, the input-coupling capacitor is

charged to the preamplifier’s DC-bias voltage through

the RF of the MAX4411, resulting in a DC shift across

the capacitor and an audible click/pop. Delaying the

rise of the SHDN_ signals 4 to 5 time constants (80ms

to 100ms) based on RIN and CIN, relative to the startup

of the preamplifier, eliminates this click/pop caused by

the input filter.

Applications Information

Power Dissipation

Under normal operating conditions, linear power ampli-

fiers can dissipate a significant amount of power. The

maximum power dissipation for each package is given

in the Absolute Maximum Ratings section 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 QFN package is

+59.3°C/W.

The MAX4411 has two power dissipation sources, the

charge pump and the two drivers. If the power dissipa-

tion for a given application exceeds the maximum

allowed for a given package, either reduce VDD,

increase load impedance, decrease the ambient tem-

perature, or add heatsinking to the device. Large

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