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

OUTPUT POWER vs. SUPPLY VOLTAGE

300

fIN = 1kHz

250

RL = 16Ω

THD+N = 10%

INPUTS 180°

OUT OF PHASE

200

150

100

INPUTS

50

IN PHASE

0

1.8 2.1 2.4 2.7 3.0 3.3 3.6

SUPPLY VOLTAGE (V)

Figure 5. Output Power vs. Supply Voltage with Inputs In/Out of

Phase

output, supply, and ground traces improve the maxi-

mum power dissipation in the package.

Thermal-overload protection limits total power dissipa-

tion in the MAX4411. When the junction temperature

exceeds +140°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 thermal-

overload conditions.

Output Power

The device has been specified for the worst-case sce-

nario—when both inputs are in phase. Under this con-

dition, 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 magnitude and

phase, subsequently leading to an increase in the max-

imum attainable output power. Figure 5 shows the two

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

available power lies between these extremes.

Powering Other Circuits from a

Negative Supply

An additional benefit of the MAX4411 is the internally

generated, negative supply voltage (PVSS). This volt-

age provides the ground-referenced output level. PVSS

can, however, also be used to power other devices

within a design limit current drawn from PVSS to 5mA;

exceeding this affects the headphone driver operation.

A typical application is a negative supply to adjust the

contrast of LCD modules.

PVSS is roughly proportional to PVDD and is not a regu-

lated voltage. The charge-pump output impedance

must be taken into account when powering other

devices from PVSS. The charge-pump output imped-

ance plot appears in the Typical Operating

Characteristics. For best results, use 2.2µF charge-

pump capacitors.

Component Selection

Input Filtering

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

nal RIN, forms a highpass filter that removes the DC

bias from an incoming signal (see Typical Application

Circuit). 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 the CIN

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

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

frequency response. Use capacitors whose dielectrics

have low-voltage coefficients, such as tantalum or

aluminum electrolytic ones. Capacitors with high-voltage

coefficients, such as ceramics, may result in increased

distortion at low frequencies.

Charge-Pump Capacitor Selection

Use capacitors with an ESR less than 100mΩ 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. Table 1 lists sug-

gested manufacturers.

Flying Capacitor (C1)

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

pump’s load regulation and output resistance. A C1

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

provide sufficient current drive, which leads to a loss of

output voltage. Increasing the value of C1 improves

load regulation and reduces the charge-pump output

resistance to an extent. See the Output Power vs.

Charge-Pump Capacitance and Load Resistance

graph in the Typical Operating Characteristics. Above

2.2µF, the on-resistance of the switches and the ESR of

C1 and C2 dominate.

Hold Capacitor (C2)

The hold capacitor value and ESR directly affect the

ripple at PVSS. Increasing the value of C2 reduces

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