MAX9722B(2003) データシートの表示（PDF） - Maxim Integrated

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MAX9722B
(Rev.:2003)

5V, Differential Input, DirectDrive, 130mW Stereo Headphone Amplifiers with Shutdown

Maxim Integrated 

5V, Differential Input, DirectDrive, 130mW

Stereo Headphone Amplifiers with Shutdown

Detailed Description

The MAX9722A/MAX9722B stereo headphone amplifiers

feature Maxim’s patented DirectDrive architecture, elimi-

nating the large output-coupling capacitors required by

conventional single-supply headphone amplifiers. The

devices consist of two class AB headphone amplifiers,

undervoltage lockout (UVLO)/shutdown control, charge

pump, and comprehensive click-and-pop suppression

circuitry (see Typical Application Circuit). The charge

pump inverts the positive supply (PVDD), creating a neg-

ative supply (PVSS). The headphone amplifiers operate

from these bipolar supplies with their outputs biased

about GND (Figure 1). The benefit of this GND bias is

that the amplifier outputs do not have a DC component,

typically VDD/2. The large DC-blocking capacitors

required with conventional headphone amplifiers are

unnecessary, thus conserving board space, reducing

system cost, and improving frequency response. The

device features an undervoltage lockout that prevents

operation from an insufficient power supply and click-

and-pop suppression that eliminates audible transients

on startup and shutdown. Additionally, the MAX9722A/

MAX9722B feature thermal-overload and short-circuit

protection and can withstand ±8kV ESD strikes at the

output pins.

Differential Input

The MAX9722 can be configured as a differential input

amplifier (Figure 2), making it compatible with many

CODECs. A differential input offers improved noise

immunity over a single-ended input. In devices such as

cellular phones, high-frequency signals from the RF

transmitter can couple into the amplifier’s input traces.

The signals appear at the amplifier’s inputs as com-

mon-mode noise. A differential input amplifier amplifies

the difference of the two inputs, and signals common to

both inputs are cancelled. Configured differentially, the

gain of the MAX9722 is set by:

AV = RF1/RIN1

RIN1 must be equal to RIN2, and RF1 must be equal to

RF2.

The common-mode rejection ratio (CMRR) is limited by

the external resistor matching. For example, the worst-

case variation of 1% tolerant resistors results in 40dB

CMRR, while 0.1% resistors result in 60dB CMRR. For

best matching, use resistor arrays.

The RIN1 and RF1 of the MAX9722B are internal, set

RIN2 = 15kΩ and RF2 = 30kΩ. However, for best

results, use the MAX9722A.

VDD

VOUT

VDD/2

GND

CONVENTIONAL DRIVER-BIASING SCHEME

+VDD OR 3V

VOUT

GND

-VDD OR -3V

DirectDrive BIASING SCHEME

Figure 1. Conventional Driver Output Waveform vs. MAX9722A/

MAX9722B Output Waveform

RF1*

RIN1*

IN-

OUT

RIN2

IN+

RF2

RIN1 = RIN2, RF1 = RF2

*RIN1 AND RF1 ARE INTERNAL FOR MAX9722B.

Figure 2. Differential Input Configuration

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