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

IN_

BIAS

OUT_+

BIAS

VOUT

VDD

VDD / 2

GND

CONVENTIONAL DRIVER-BIASING SCHEME

+VDD

OUT_-

BIAS

GND

GND

Figure 1. MAX9779 Signal Path

HPOUT_

-VDD

DirectDrive BIASING SCHEME

Figure 2. Traditional Headphone Amplifier Output Waveform

vs. DirectDrive Headphone Amplifier Output Waveform

Detailed Description

The MAX9779 combines a 2.6W BTL speaker amplifier

and a 110mW DirectDrive headphone amplifier with

integrated headphone sensing and comprehensive

click-and-pop suppression. The MAX9779 features four-

level gain control. The device features high 90dB PSRR,

low 0.01% THD+N, industry-leading click-pop perfor-

mance, and a low-power shutdown mode.

Each signal path consists of an input amplifier that sets

the gain of the signal path and feeds both the speaker

and headphone amplifier (Figure 1). The speaker

amplifier uses a BTL architecture, doubling the voltage

drive to the speakers and eliminating the need for DC-

blocking capacitors. The output consists of two signals,

identical in magnitude, but 180° out of phase.

The headphone amplifiers use Maxim’s patented

DirectDrive architecture that eliminates the bulky output

DC-blocking capacitors required by traditional head-

phone amplifiers. A charge pump inverts the positive

supply (CPVDD), creating a negative supply (CPVSS).

The headphone amplifiers operate from these bipolar

supplies with their outputs biased about GND (Figure 2).

The amplifiers have almost twice the supply range

compared to other single-supply amplifiers, nearly qua-

drupling the available output power. The benefit of the

GND bias is that the amplifier outputs no longer have a

DC component (typically VDD / 2). This eliminates the

large DC-blocking capacitors required with convention-

al headphone amplifiers, conserving board space and

system cost, and improving frequency response.

The device features an undervoltage lockout that pre-

vents operation from an insufficient power supply and

click-and-pop suppression that eliminates audible tran-

sients on startup and shutdown. The amplifiers include

thermal-overload and short-circuit protection, and can

withstand ±8kV ESD strikes on the headphone amplifier

outputs (IEC air discharge). An additional feature of the

speaker amplifiers is that there is no phase inversion

from input to output.

DirectDrive

Conventional single-supply headphone amplifiers have

their outputs biased about a nominal DC voltage (typi-

cally half the supply) for maximum dynamic range.

Large coupling capacitors are needed to block this DC

bias from the headphones. 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 amplifier.

Maxim’s patented DirectDrive architecture uses a charge

pump to create an internal negative supply voltage. This

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