Stereo Analog Subsystem for Mobile Handsets

NationalSemiconductor Corp.'s stereo analogsubsystemwith integrated Class G headphone amplifier and automatic level control (ALC)is for smartphones and feature phones. The PowerWise LM49251's Class Gheadphone amp reduces the supply voltage to lower power consumption and extendaudio (MP3, movies, etc.) playback time. The loudspeaker's ALC providesdesigners with options to control audio distortion levels and prevent speakerdamage.

National's LM49251 stereo analog subsystem combines a 1.4W ClassD speaker amplifier, 20 mW Class G headphone amplifier and ALC in a 2.55 by3.02 mm package. The LM49251 offers low power consumption, consuming less than7 mA of quiescent current at 3.3V for the loudspeaker and headphone. TheLM49251's ALC feature provides designers with a programmable output powerlimiter 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-widthmodulation (PWM) architecture that significantly reduces RF emissions whilepreserving audio quality. The LM49251's Class G headphone architecturesignificantly increases audio playback time with its adaptive power supplyapproach, enabling low supply rails.

The LM49251'sno-clip ALC feature prevents distortion as battery voltages drop, allowingsmall signals to be amplified at high gains while preventing clipping ofhigh-level signals. Its multiple inputs provide configurability for addressingdifferent system requirements, and the LM49251's mode selection, shutdown andvolume are controlled through an I2C compatible interface. The IC'sclick-and-pop suppression eliminates audible transients on power up and duringshutdown.

National alsointroduced the LM49153 mono audio subsystem,which includes the same features as the LM49251, while integrating noise gatefunctionality onto the Class D amplifier. The noise gate feature prevents noisefrom being amplified when the volume is turned up. The LM49153 is offered in a25-bump, 2.30 by 2.42 mm, micro SMD package.

Stereo Analog Subsystem for Mobile Handsets