PowerWise LM49251, the first integrated Class G headphone amplifier analog subsystem

National Semiconductor Corp. has announced the industry's first integrated Class G headphone amplifier and automatic level control (ALC) for stereo analog subsystems in smart and feature-rich phones. The PowerWise LM49251 analog subsystem features a Class G headphone amplifier that dynamically reduces the supply voltage to save power, thereby extending the playback time of audio (MP3, movie, etc.) systems. The speaker's built-in automatic level control function provides system designers with multiple options to flexibly control audio system distortion and avoid speaker damage.

　　National Semiconductor's LM49251 stereo analog subsystem has a built-in 1.4W Class D speaker amplifier and 20mW Class G headphone amplifier in an ultra-small 2.55mm x 3.02mm package, and also has an automatic level control function. The LM49251 has lower power consumption than similar products, and its quiescent current does not exceed 7mA if the speaker and headphones run at 3.3V. In addition, the LM49251's automatic level control function allows engineers to use programmable output power limiters to protect speakers and select the amplitude of the limiting level.

　　LM49251 Stereo Analog Subsystem – Key Technical Features

　　The LM49251 subsystem in a 30-ball micro SMD package has an enhanced electromagnetic radiation suppression (E2S) circuit and a Class D amplifier that uses National Semiconductor's patented ultra-low electromagnetic interference pulse width modulation (PWM) architecture to significantly reduce the amount of radio frequency radiation to ensure that the audio signal is free from interference. The LM49251's Class G headphone amplifier has an adjustable power supply path, which greatly extends the playback time of the audio system and reduces the power supply voltage to an extremely low level. At the same time, its power conversion efficiency is almost twice that of a traditional Class AB headphone amplifier.

　　The LM49251 subsystem features automatic level control without distortion, ensuring that there is no signal distortion when the battery voltage drops, so that small signals can be amplified with a larger gain multiple while preventing high-frequency signals from being clipped. This subsystem has multiple input interfaces, so engineers can configure it appropriately according to different system requirements. In addition, the LM49251 mode options, shutdown, and volume can be controlled through the I2C compatible interface. The switch/switching noise suppression function of this chip can eliminate the human ear-discernible noise generated at the moment of startup and shutdown.

　　In addition, National Semiconductor also launched the LM49153 mono audio subsystem, which has the characteristics of retaining the original functions of the LM49251 and its Class D amplifier also has a noise gating function. Whenever the volume of the speaker is turned up, the noise gating function will suppress the noise to avoid amplifying the noise. The LM49153 subsystem adopts a 25-bump micro SMD package with a size of only 2.30mm x 2.42mm.

　　Pricing and Availability

　　The LM49251 stereo analog subsystem is priced at $1.60 per unit, while the LM49153 mono analog subsystem is priced at $1.50 per unit. Both chips are available in quantities of 1,000 and are available now.