Class D Audio Subsystems simplify portable product designs.

Press Release Summary:

Mixed-signal audio subsystem (LM49352) integrates audio codec functionality with ground-referenced headphone amps, earpiece driver, Class D loudspeaker, and audio DSP in 3.3 x 3.3 mm package. Analog subsystem (LM49151) integrates earpiece driver, Class D loudspeaker, ground-referenced headphone amps, and automatic level control (ALC) in 2.2 x 2.6 mm package. Applications include smart phones, full-featured phones, portable gaming devices, and portable GPS devices.

Original Press Release:

National Semiconductor Extends Family of Low-Power, Premium Quality Audio Subsystems for Handheld Devices

PowerWise Audio Subsystems Simplify Portable Product Design

GLOBALPRESS ELECTRONICS SUMMIT, SAN FRANCISCO - March 31, 2009 - National Semiconductor Corp. (NYSE:NSM) today announced it has extended its family of low-power Boomer® Class D audio subsystems with two premium quality devices that simplify portable product design. The LM49352 mixed-signal audio subsystem and LM49151 analog subsystem are targeted at smart phones, full-featured phones, portable gaming devices and portable GPS devices. National will demonstrate these PowerWise® energy-efficient subsystems at the GlobalPress Electronics Summit in San Francisco, Calif., from March 31 to April 1.

The LM49352 is a mixed-signal audio subsystem that integrates audio codec functionality with ground-referenced headphone amplifiers, earpiece driver, Class D loudspeaker and audio digital signal processor (DSP) in one miniature 3.3 mm by 3.3 mm package. The loudspeaker delivers ultra-high efficiency (93 percent at 970 mW from a 4.2V supply), while the headphone amplifier offers low-power (18 mW) MP3 playback to extend battery life.

The LM49151 analog subsystem integrates an earpiece driver, Class D loudspeaker, ground-referenced headphone amplifiers and automatic level control (ALC) in an ultra-small 2.2 mm by 2.6 mm package. The LM49151 offers the lowest power in its class, consuming 7.3 mA of quiescent current at 3.3V for the loudspeaker and headphone. The subsystem's ALC feature provides handset manufacturers with a variety of options to control audio distortion levels and prevent speaker damage.

Key Technical Features - LM49352 Audio Mixed-Signal Subsystem Offered in a 36-bump micro SMDxt package, the LM49352 is a complete audio subsystem that includes stereo 24-bit digital-to-analog converters (DACs) and stereo 24-bit analog-to-digital converters (ADCs), stereo headphone amplifier and a low electromagnetic interference (EMI) Class D loudspeaker amplifier. The device features a dual bi-directional I2S interface and PCM audio bridge to enable easy interface to peripherals such as Bluetooth® modules, as well as an I2C compatible interface for programming different gains and modes.

The LM49352's stereo ADC provides a signal-to-noise ratio (SNR) of 97 dB with a 24-bit, 48 kHz signal and the DAC provides an SNR of 103 dB with a 24-bit, 48 kHz signal. The loudspeaker amplifier delivers up to 970 mW to an 8-Ohm load with less than one percent harmonic distortion plus noise (THD+N) at 4.2V.

The LM49352's digital signal processing includes dedicated effects circuits for both the DACs and ADCs. These circuits include volume control, ALC with compression and limiting, and 5-band equalization (EQ) for quality audio processing. The ADC also is equipped with a flexible wind noise filter that can operate in voice or high fidelity recording mode.

Key Technical Features - LM49151 Analog Audio Subsystem Offered in a 20-bump micro SMD package, the LM49151 audio subsystem includes a mono, enhanced emission suppression (E2S), Class D loudspeaker amplifier, Class AB earpiece driver, stereo ground-referenced headphone drivers, volume control, input mixer/multiplexer and speaker protection. The Class D amplifier features a patented, ultra-low EMI pulse-width modulation (PWM) architecture that significantly reduces RF emissions while preserving audio quality.

The LM49151's ALC provides multiple benefits. Its no-clip ALC feature prevents distortion as battery voltages drop by allowing small signals to be amplified at high gains, while preventing clipping of high-level signals. In addition, the LM49151's clip-level select ALC produces high output power at a controlled distortion level, while the power-level select ALC provides speaker protection.

Pricing and Availability
Available now, the LM49352 is priced at $7.55 each and the LM49151 is priced at $1.60 each. All prices are in 1,000-unit quantities. For more information on the LM49352, or to order samples and an evaluation board, visit For more information on the LM49151, or to order samples and an evaluation board, visit

About National's Audio Portfolio
National Semiconductor has been a leading provider of audio solutions for more than 30 years and offers a wide range of products in its Boomer®, Overture® and high-performance audio lines. National works with every major handset maker in the world and is the leading provider of analog audio solutions for the cell phone market. The company's line of Boomer audio amplifiers and subsystems enhance and enrich the entire range of sound - from voice, ring sounds and music - that can be amplified in mobile phones and other portable equipment. National manufactures Class AB and Class D speaker amplifiers, headphone amplifiers and audio subsystems for many applications ranging from portable devices to high-power, high-fidelity audio systems. The company offers its higher-power Overture amplifiers for mid-performance consumer applications, and National's new high-performance series brings dramatically improved sound quality to high-fidelity consumer and professional audio equipment. Fo r more information on National's audio products, visit

About National Semiconductor
National Semiconductor creates energy-efficient analog and mixed-signal semiconductors. Its PowerWise® products enable systems that consume less power, extend battery life and generate less heat. Headquartered in Santa Clara, Calif., National reported sales of $1.89 billion for fiscal 2008 which ended May 25, 2008. Additional company and product information is available at

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