Wednesday, January 23, 2008

National Semiconductor LME49600 audio buffer

National Semiconductor claims its new audio buffer 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.

Other applications include line drivers, analogue-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.

According to the company, 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 just 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

The LME49600 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 is available at

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