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National Semiconductor Introduces Adjustable Buck Regulator Controller for High-Current Applications

Feb 9, 2005

February 9, 2005—National Semiconductor Corporation (NYSE:NSM) today announced the LM2657, an adjustable 200 kHz to 500 kHz dual-channel, voltage-mode-controlled, high-speed synchronous buck regulator controller ideal for high-current applications.

The LM2657 requires only N-channel FETs for both the upper and lower positions of each stage. It features line feed-forward to improve the response to input transients. At very light loads, the user can choose between the high-efficiency pulse-skip mode or the constant frequency forced-PWM mode. Loss-less current limiting without the use of external sense resistors is made possible by sensing the voltage drop across the bottom FET. A unique adaptive duty cycle clamping technique is incorporated to significantly reduce peak currents under abnormal load conditions. The two independently programmable outputs switch 180 degrees out of phase (interleaved switching), reducing the input capacitor and filter requirements. The input voltage range is 4.5 V to 28 V, while the output voltages are adjustable down to 0.6 V.

The LM2657’s Features and Benefits

  • Switching frequency adjustable from 200 kHz to 500 kHz
  • Input voltage range from 4.5 V to 28 V
  • Synchronous dual-channel interleaved switching
  • Forced-PWM or pulse-skip modes
  • Loss-less bottom-side FET current sensing
  • Adaptive duty cycle clamp
  • High-current N-channel FET drivers
  • Low shutdown supply current
  • Reference voltage accurate to within ±1.5 percent
  • Output voltage adjustable down to 0.6 V
  • Power good flag and chip enable
  • Under-voltage lockout
  • Over-voltage/under-voltage protection
  • Soft-start

About National’s Power Management Products
National Semiconductor is the number one supplier of power management ICs with 12.8 percent market share, according to iSuppli’s 2004 voltage regulator/reference survey.  National’s power management revenue grew 29.7 percent in 2003 over the previous year, compared to 17.3 percent growth for the industry during the same time period.  National's innovative power management products include best-in-class linear regulators; power monitoring, control and reference ICs; and switching converters, such as high-voltage ICs for DC/DC conversion, switched capacitor converters, lighting management ICs and inductive switching converters.  National's WEBENCH® online design tool allows designers to select a power management product, create and analyze a design, and then build custom prototypes that can be delivered within 24 hours.  More information about National’s power management products is available at http://power.national.com

Pricing and Availability
The LM2657, in a TSSOP-28 package, is available now and priced at $2.75 each in 1,000-unit quantities.

About National Semiconductor
National Semiconductor, the industry's premier analog company, creates high-performance analog devices and subsystems.  National's leading-edge products include power management circuits, display drivers, audio and operational amplifiers, communication interface products and data conversion solutions. National's key markets include wireless handsets, displays, PCs and laptops.  The company's analog products are also optimized for numerous applications in a variety of electronics markets, including medical, automotive, industrial, and test and measurement.  Headquartered in Santa Clara, California, National reported sales of $1.98 billion for fiscal 2004, which ended May 30, 2004.  Additional company and product information is available at www.national.com