National
Semiconductor Corp.'s stereo analog
subsystem
with integrated Class G headphone amplifier and automatic level control (ALC)
is for smartphones and feature phones. The PowerWise LM49251's Class G
headphone amp reduces the supply voltage to lower power consumption and extend
audio (MP3, movies, etc.) playback time. The loudspeaker's ALC provides
designers with options to control audio distortion levels and prevent speaker
damage.
National's LM49251stereo analog subsystem combines a 1.4W Class
D speaker amplifier, 20 mW Class G headphone amplifier and ALC in a 2.55 by
3.02 mm package. The LM49251 offers low power consumption, consuming less than
7 mA of quiescent current at 3.3V for the loudspeaker and headphone. The
LM49251's ALC feature provides designers with a programmable output power
limiter for speaker protection and clip level select.
Offered in a 30-bump micro SMD package, the LM49251 provides enhanced Emission Suppression
(E2S) and a Class D amplifier featuring a patented, ultra-low EMI pulse-width
modulation (PWM) architecture that significantly reduces RF emissions while
preserving audio quality. The LM49251's Class G headphone architecture
significantly increases audio playback time with its adaptive power supply
approach, enabling low supply rails.
The LM49251's
no-clip ALC feature prevents distortion as battery voltages drop, allowing
small signals to be amplified at high gains while preventing clipping of
high-level signals. Its multiple inputs provide configurability for addressing
different system requirements, and the LM49251's mode selection, shutdown and
volume are controlled through an I2C compatible interface. The IC's
click-and-pop suppression eliminates audible transients on power up and during
shutdown.
National also
introduced the LM49153 mono audio subsystem,
which includes the same features as the LM49251, while integrating noise gate
functionality onto the Class D amplifier. The noise gate feature prevents noise
from being amplified when the volume is turned up. The LM49153 is offered in a
25-bump, 2.30 by 2.42 mm, micro SMD package.
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