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National Semiconductor Introduces Very Small, Highly Efficient Synchronous Step-up DC-DC Converters with True Shutdown Isolation

Nov 16, 2006

November 16, 2005 - National Semiconductor Corporation (NYSE:NSM) today introduced two fixed-frequency step-up DC-DC converters with true shutdown isolation.  Packaged in a very small 8-bump micro SMD, the LM3500 and LM3501 are well-suited for driving white LEDs in display backlighting and other lighting applications.

The converters feature a low feedback voltage of 500 mV and fully integrated synchronous switching that requires no external Schottky diode.  Power efficiency has been optimized for lighting applications in portable products with single cell Li-Ion or 3-cell NiMH battery supplies.  The LM3500 and LM3501 operate with a fixed 1 MHz switching frequency and ceramic input and output capacitors.  High switching frequency, very small external ceramic capacitors and the integration of a diode, provides the customer with a small, low-cost solution.

A single external resistor is used to set the maximum LED current in driver applications.  The current can easily be adjusted using a pulse-width modulation (PWM) signal on the shutdown pin of the LM3500 or an analog control signal on the CNTRL pin of the LM3501.  In shutdown, the converters completely disconnect the input from the output, creating total isolation and preventing any leakage currents from trickling into the LEDs.

Key features for the LM3500 and LM3501 include:

  • Synchronous rectification, high efficiency and no external Schottky diode required       
  • 80 percent efficiency       
  • PWM (LM3500) or analog (LM3501) dimming control       
  • Uses small surface mount components       
  • Can drive two to five white LEDs in series       
  • 2.7V to 7V input range       
  • Internal output over-voltage protection (OVP) circuitry       
  • True shutdown isolation       
  • Requires only small ceramic capacitors at the input and output       
  • Thermal shutdown       
  • 0.1 µA shutdown current

About National’s Power Management Products
National Semiconductor is the number one supplier of power management ICs with 14.1 percent market share, according to iSuppli’s 2005 voltage regulator/reference survey.  National’s power management revenue grew 37.3 percent in 2004 over the previous year, compared to 24 percent growth for the industry.  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 also offers online tools that enable power designers to select the best power management chips for their applications.  National's WEBENCH® design tool allows designers to choose a product, create and analyze a design, and then build custom prototypes that can be delivered within 24 hours.

Packaging, Pricing and Availability
National’s LM3500 and LM3501 are available now in an 8-bump micro SMD package.  The LM3500 costs $1.40 and the LM3501 costs $1.51 in quantities of 1,000.  Lead-free package options are also available.

For more information about the LM3500 or to order samples, visit http://www.national.com/pf/LM/LM3500.html.  For an evaluation board, visit http://www.national.com/store/view_item/index.html?nsid=LM3500TL-16EV.

For more information about the LM3501 or to order samples, visit http://www.national.com/pf/LM/LM3501.html.  For an evaluation board, visit http://www.national.com/store/view_item/index.html?nsid=LM3501TL-16EV.

For more information on National’s white LED driver products, visit power.national.com.  National’s WEBENCH online design tool supports a large selection of white LED drivers.  To explore these solutions, visit http://webench.national.com.  To learn more about designing with white LED drivers, visit National’s library of online seminars

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, communication interface products and data conversion solutions. National's key analog markets include wireless handsets, displays and a variety of broad electronics markets, including medical, automotive, industrial, and test and measurement applications. Headquartered in Santa Clara, California, National reported sales of $1.91 billion for fiscal 2005, which ended May 29, 2005.  Additional company and product information is available at www.national.com