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National Semiconductor Introduces Industry's Lowest-Noise Audio Buffer

LME49600 Accurately Reproduces High-Dynamic Input Signals without Adding Distortion

Jan 21, 2008

January 21, 2008 – A new buffer from National Semiconductor Corporation (NYSE: NSM) delivers the industry’s lowest noise and harmonic distortion for professional audio applications. Part of National’s high-fidelity LME™ audio amplifier family, the LME49600 produces the necessary output current to drive multiple low-impedance headphones and the voltage swing to drive several high-impedance headphones. Additionally, the buffer is well-suited for a wide range of other applications, including line drivers, analog-to-digital converter (ADC) input drivers, low-noise and wide-frequency voltage regulators, and it can also drive the headphone amplifier output stage in mixer consoles as well as capacitive loads in low-power audio amplifiers.

The LME49600’s high-fidelity specifications ensure that it can respond to highly dynamic inputs, accurately reproducing these signals without degrading them by adding distortion. The device delivers 180 MHz bandwidth, a high slew rate of 2000 V/us and has 2.6 nV/rtHz input referred voltage noise density. In a closed-loop configuration with National’s LME49710 single operational amplifier (op amp), the total harmonic distortion plus noise (THD+N) is a vanishingly low 0.00003 percent. Combining the LME49600’s +/- 250 mA output current capacity with the LME49710 and an LM4040 low-noise bandgap reference produces a very high-performance, low-noise, wide-bandwidth, audiophile quality, voltage regulator.

National engineers developed the LME49600 using the company’s proprietary VIP3 process technology. The high-voltage, high-performance, complementary bipolar technology, with vertically integrated NPN and PNP transistors, enables larger peak-to-peak output voltage swings that are well-suited for high-voltage requirements in high-end audio applications. 

Key Technical Features – LME49600 High-Current Audio Buffer
The LME49600 is a high-performance, low-distortion, high-fidelity audio headphone buffer that can continuously source or sink 250 mA. Designed for use inside an op amp’s feedback loop, it increases output current, improves capacitive load drive and eliminates thermal feedback. The LME49600 offers pin-selectable bandwidth, including a low current, 110 MHz bandwidth-mode that consumes 8 mA and a wide 180 MHz bandwidth-mode that consumes 15 mA. In both modes, the LME49600 has a nominal 2000 V/us slew rate. Bandwidth is easily adjusted by either leaving the bandwidth-control pin unconnected or connecting a resistor between the bandwidth pin and the emitter voltage pin. The device’s supply voltage range is +/- 2.25V to +/- 18V. The LME49600 is fully protected through internal current limit and a thermal shutdown that activates when the junction temperature exceeds 150 degrees C.

Pricing and Availability
The LME49600 is available now in a 5-lead TO-263 surface mount package and is priced at $4.50 each in 1000-unit quantities. More information, easy-to-order samples and evaluation boards are available at http://www.national.com/pf/LM/LME49600.html.

Note to editors:  To view a high-resolution downloadable photo of this product, visit National's photo gallery.

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. For more information on National’s audio products, visit http://www.national.com/audio.

About National Semiconductor
National Semiconductor, the industry's premier analog company, creates high-value analog devices and subsystems. National's leading-edge products include power management circuits, display drivers, audio and operational amplifiers, interface products and data conversion solutions. National's key analog markets include wireless handsets, displays, communications infrastructure, medical, automotive, industrial, and test and measurement applications. Headquartered in Santa Clara, Calif., National reported sales of $1.93 billion for fiscal 2007, which ended May 27, 2007. Additional company and product information is available at www.national.com.