Datasheet

MAX4298/MAX4299
Ultra-High PSRR Stereo Drivers +
Microphone Amp + 100mA Linear Regulator
8 _______________________________________________________________________________________
The amplifiers exhibit better than 115dB of DC power-
supply rejection and 93dB at 20kHz. The output ampli-
fiers are capable of driving a 1.5V
RMS
signal into 10kΩ
load with 0.0008% distortion. They can also drive 32Ω
headphones to 1.2V
RMS
with 0.02% distortion. At
+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 50kΩ.
Clickless/Popless Function
The MAX4298/MAX4299 are designed for high-fidelity
audio performance into AC-coupled loads. The design
techniques achieve a clickless/popless power-up
sequence, and the use of a low-current standby supply
(SV
CC
) or external Schottky diode/reservoir capacitor
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
V
CC
or GND. MUTE only affects the headphone driver
outputs. REG, BIAS, and MICOUT are unaffected. OUT1
and OUT2 are muted, but remain in a low-impedance
state to ensure clickless/popless operation.
SV
CC
The MAX4298/MAX4299 provide a fully clickless power-
down sequence. SV
CC
normally should be connected to
a low-current +5V power source, but alternatively can be
connected with a reservoir capacitor to ground and a
Schottky diode to V
CC
. A reservoir capacitor of 220µF or
higher provides enough charge for the clickless power-
down sequence when C
BIAS
= 1µF. For larger values of
C
BIAS
, increase the reservoir capacitor accordingly.
Short to V
CC
if clickless power-down is not needed.
Driver Amplifier
The headphone driver amplifier is a class AB amplifier
designed to drive 16Ω 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.
C
BYPASS
IN1
V
CC
SV
CC
OUT1
MUTE
OUT2
GND
MAX4298
IN2
BIAS
+
_
50kΩ
2.25V
_
+
Figure 1. MAX4298 Block Diagram
C
BYPASS
OUT1
MICIN
GND
MAX4299
MICOUT
MUTE
IN2
BIAS
IN1
1.233V
FB
V
CC
SV
CC
REGON
REG
18.4kΩ
11kΩ
50kΩ
OUT2
N.C.
_
+
2.25V
+
_
+
_
+
_
PGND
Figure 2. MAX4299 Block Diagram