MAX4298ESD+T Maxim Integrated Products, MAX4298ESD+T Datasheet - Page 9

• Manufacturer Part Number: MAX4298ESD+T
• Description: IC STEREO DVR AUDIO 14-SOIC
• Manufacturer: Maxim Integrated Products
• Type: PSRR Stereo Driverr

Specifications of MAX4298ESD+T

• Applications: Desktop Audio, MP3, USB
• Mounting Type: Surface Mount
• Package / Case: 14-SOIC (3.9mm Width), 14-SOL
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX4299 also has an additional 100mA low-
dropout (LDO) regulator to provide clean analog power
for other sensitive analog circuitry on the PC board,
such as a typical PC99 audio codec or microphone
biasing. It is designed to provide good AC line regula-
tion. The nominal output voltage of REG is 3.3V, and is
adjustable between 1.2V and 4.5V by connecting a
resistor-divider from REG to GND. Connect FB to the
junction of the resistor-divider. The input impedance at
FB is typically 7k , which should be considered in out-
put voltage calculations. REG should be bypassed to
GND with at least 10µF.
Normally, use a 10µF capacitor on REG (MAX4299 only)
and a 1µF capacitor on C
ues and lower ESRs provide better supply-noise rejec-
tion and line-transient response. Reduce noise and
improve load-transient response, stability, and power-
supply rejection by using larger capacitors. For stable
operation over the full temperature range and load cur-
rents up to 100mA, a minimum of 10µF (REG) and 1µF
(C
Use a 1µF bypass capacitor on BIAS to ensure a fully
clickless/popless power-up sequence. Smaller capacitor
values may be used here to decrease the power-up
time, but may cause the power-up transient to become
audible. Larger bypass capacitors are not necessary to
reduce noise and/or improve AC power-supply rejection.
SV
diode for charging, a 220µF reservoir capacitor on
SV
down sequence. Smaller capacitors here may cause an
audible output transient on power-down; 220µF or high-
er provides enough energy when C
er values of C
accordingly.
Common microphone elements require resistive biasing
to power their internal circuitry. A 2k resistor is typical-
ly used, and the microphone is AC-coupled to the
microphone amplifier. If the microphone element allows
low-voltage operation, biasing to the REG output pro-
vides excellent power-supply rejection.
The excellent PSRR of the MAX4298/MAX4299 allows
them to operate from noisy power supplies. In most
applications, a 0.1µF capacitor from V
ficient. This bypass capacitor should be placed close
to the V
BYPASS
CC
CC
is the standby power supply. If using an external
provides standby power for the clickless power-
CC
) is recommended.
Microphone Amp + 100mA Linear Regulator
pin.
BIAS
Applications Information
_______________________________________________________________________________________
Power Supply and Bypassing
, increase the reservoir capacitor
Capacitor Selection and
BYPASS
Mic Biasing (MAX4299)
Regulator (MAX4299)
Regulator Stability
. Larger capacitor val-
BIAS
Ultra-High PSRR Stereo Drivers +
CC
= 1µF. For larg-
to GND is suf-
Good layout improves performance by decreasing the
amount of stray capacitance and noise at the power
amplifier’s inputs and output. To decrease stray capaci-
tance, minimize PC board trace lengths and resistor
leads, and place external components as close to the
pins as possible.
The first equation below indicates the maximum power
dissipation point for a package that has two power
amplifiers operating at identical known supply voltages
and loads with sine wave inputs:
For example, with a 5V power supply and a load of 16 ,
the maximum power dissipation of the amplifiers alone
is 317mW.
The additional power dissipation due to the 100mA reg-
ulator operating at maximum current is nominally
170mW, but will increase if the output is reduced exter-
nally from its nominal 3.3V. The regulator power con-
sumption is given by:
To avoid thermal shutdown the sum of the regulator and
amplifier power dissipation must not exceed the absolute
maximum power-dissipation rating of the package.
The MAX4298/MAX4299 have short-circuit current pro-
tection on all outputs. They also have a thermal shut-
down function designed to protect the chip from junction
temperatures in excess of +150°C that may arise from
temporary short circuits or operation beyond the power
dissipation limit of the package. The driver amplifier out-
puts limit at around ±220mA, the regulator at 150mA,
and the microphone amplifier at +1.5mA/-12mA.
Universal serial bus (USB) interfaces are an increasingly
popular method of interfacing medium-speed (up to
12Mbps) PC peripherals. One of the great benefits of
the USB interface is the inclusion of a +5V supply. While
this supply works well for a mouse or keyboard, its sus-
ceptibility for noise pickup can be unsuitable for high-
fidelity audio applications. The MAX4298/MAX4299s’
excellent PSRR make them ideal candidates for USB
applications due to their insensitivity to the supply noise.
Of particular interest is an Internet-Protocol (IP) phone.
This PC peripheral uses the local internet service
provider as a free long-distance phone. The MAX4299,
with its integral microphone amp, headphone driver,
and linear regulator, can be a key element in the imple-
mentation of an IP phone that interfaces to the PC
through the USB.
P
REG
P
IC(DISS)
= (V
Short-Circuit Protection and
CC
= (V
- V
CC
REG
)
2
) x 100mA [W]
/ (
Thermal Shutdown
Power Dissipation
USB Applications
2
R
L
) [W]
Layout
9