Ultra-High PSRR Stereo Drivers +

Microphone Amp + 100mA Linear Regulator

8

_______________________________________________________________________________________

MAX4298 block diagram and Figure 2 is the MAX4299

block diagram.

The amplifiers exhibit better than 115dB of DC power-

supply rejection and 93dB at 20kHz. The output ampli-

load with 0.0008% distortion. They can also drive 32

Ω

+3.3V, the linear regulator can output 100mA of current.

BIAS

The common-mode bias point for the amplifiers is set to

2.25V by internal circuitry that has two functions. It pro-

vides a clickless/popless power-up/power-down wave-

form for the amplifiers. Also, it generates a ground-

referenced bias voltage with ultra-high power-supply

rejection ratio (PSRR). BIAS should be bypassed with 1µF

to GND.The output impedance of the BIAS pin is 50k

Ω.

Clickless/Popless Function

The MAX4298/MAX4299 are designed for high-fidelity

audio performance into AC-coupled loads. Patented

design techniques achieve a clickless/popless power-up

sequence, and the use of a low-current standby supply

combination allows clickless/popless power-down. A

clickless/popless mute function is also provided to main-

tain a low impedance output when the input signal is

switched off.

Mute Function

The MAX4298/MAX4299 have a MUTE pin that allows the

user to mute the outputs of the device. This feature dis-

connects the input signal from the power amplifiers when

a logic high is present at the MUTE pin. To ensure proper

functionality, the MUTE pin should always be tied to either

outputs. REG, BIAS, and MICOUT are unaffected. OUT1

and OUT2 are muted, but remain in a low-impedance

state to ensure clickless/popless operation.

The MAX4298/MAX4299 provide a fully clickless power-

current +5V power source or alternatively can be

connected with a reservoir capacitor to ground and a

higher provides enough charge for the clickless power-

Driver Amplifier

The headphone driver amplifier is a class AB amplifier

designed to drive 16

Ω loads. The amplifiers have innov-

ative architectures for both the input and output stages

to achieve ultra-high PSRR while maintaining rail-to-rail

output drive capability. The output stage can drive high

capacitive loads encountered when driving long cables

used for desktop speakers or headphones.

Microphone Preamplifier (MAX4299)

The MAX4299 provides a microphone preamplifier that

is a low-power version of the audio amplifier. It is intend-

ed to be used for low-level signal amplification. This

microphone preamplifier provides rail-to-rail output with

very high PSRR.

IN1

OUT1

MUTE

OUT2

GND

MAX4298

IN2

BIAS

+

_

50k

Ω

2.25V

_

+

Figure 1. MAX4298 Block Diagram

OUT1

MICIN

GND

MAX4299

MICOUT

MUTE

IN2

BIAS

IN1

1.233V

FB

REGON

REG

18.4k

Ω

11k

Ω

50k

Ω

OUT2

N.C.

_

+

2.25V

+

_

+

_

+

_

PGND

Figure 2. MAX4299 Block Diagram