MAX4411EBET(2006) 查看數據表（PDF） - Maxim Integrated

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MAX4411EBET
(Rev.:2006)

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

Maxim Integrated 

80mW, Fixed-Gain, DirectDrive, Stereo

Headphone Amplifier with Shutdown

Detailed Description

The MAX4411 fixed-gain, stereo headphone driver fea-

tures Maxim’s DirectDrive architecture, eliminating the

large output-coupling capacitors required by conven-

tional single-supply headphone drivers. The device con-

sists of two 80mW Class AB headphone drivers, internal

feedback network, undervoltage lockout (UVLO)/shut-

down control, charge pump, and comprehensive click-

and-pop suppression circuitry (see Typical Application

Circuit). The charge pump inverts the positive supply

(PVDD), creating a negative supply (PVSS). The head-

phone drivers operate from these bipolar supplies with

their outputs biased about GND (Figure 1). The drivers

have almost twice the supply range compared to other

3V single-supply drivers, increasing the available output

power. The benefit of this GND bias is that the driver out-

puts do not have a DC component typically VDD/2. The

large DC-blocking capacitors required with convention-

al headphone drivers are unnecessary, thus conserving

board space, system cost, and improving frequency

response.

Each channel has independent left/right, active-low

shutdown controls, optimizing power savings in mixed-

mode, mono/stereo operation. The device features an

undervoltage lockout that prevents operation from an

insufficient power supply and click-and-pop suppres-

sion that eliminates audible transients on startup and

shutdown. Additionally, the MAX4411 features thermal-

overload and short-circuit protection and can withstand

±8kV ESD strikes on the output pins.

Fixed Gain

The MAX4411 utilizes an internally fixed gain configura-

tion of either -1.5V/V (MAX4411) or -2V/V (MAX4411B).

All gain-setting resistors are integrated into the device,

reducing external component count. The internally set

gain, in combination with DirectDrive, results in a head-

phone amplifier that requires only five tiny 1µF capaci-

tors to complete the amplifier circuit: two for the charge

pump, two for audio input coupling, and one for power-

supply bypassing (see Typical Application Circuit).

DirectDrive

Conventional single-supply headphone drivers have their

outputs biased about a nominal DC voltage (typically half

the supply) for maximum dynamic range. Large coupling

capacitors are needed to block this DC bias from the

headphone. Without these capacitors, a significant

amount of DC current flows to the headphone, resulting

in unnecessary power dissipation and possible damage

to both headphone and headphone driver.

Maxim’s DirectDrive architecture uses a charge pump

to create an internal negative supply voltage.

VDD

VOUT

VDD/2

GND

CONVENTIONAL DRIVER-BIASING SCHEME

+VDD

VOUT

GND

-VDD

DirectDrive BIASING SCHEME

Figure 1. Conventional Driver Output Waveform vs. MAX4411

Output Waveform

This allows the MAX4411 outputs to be biased about

GND, almost doubling dynamic range while operating

from a single supply. With no DC component, there is

no need for the large DC-blocking capacitors. Instead

of two large (220µF, typ) tantalum capacitors, the

MAX4411 charge pump requires two small ceramic

capacitors, conserving board space, reducing cost,

and improving the frequency response of the head-

phone driver. See the Output Power vs. Charge-Pump

Capacitance and Load Resistance graph in the Typical

Operating Characteristics for details of the possible

capacitor sizes. There is a low DC voltage on the driver

outputs due to amplifier offset. However, the offset of

the MAX4411 is typically 0.7mV, which, when com-

bined with a 32Ω load, results in less than 23µA of DC

current flow to the headphones.

Previous attempts to eliminate the output-coupling capac-

itors involved biasing the headphone return (sleeve) to

the DC-bias voltage of the headphone amplifiers. This

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