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Industry’s First 100 V Active Clamp PWM Controller from National Semiconductor Improves Communication Systems Efficiency and Power Density

Dec 22, 2003

December 22, 2003 - Demonstrating its leadership in high-voltage power management, National Semiconductor Corporation (NYSE: NSM) today introduced an integrated 100 V pulse-width modulation (PWM) controller for forward converters with the active clamp/reset technique used in distributed power architectures.  This new device is designed for high switching frequencies and provides higher efficiencies and greater power densities than conventional forward regulators in communications, automotive, distributed and industrial power systems, and multi-output power supplies.

The active clamp technique is one of the most popular single-ended topologies used in distributed power architectures, allowing operation at duty cycles above 50 percent and higher primary to secondary turns ratios in the power transformer.  Deploying National Semiconductor’s newest high-voltage (100 V) precision analog bipolar-CMOS-DMOS process allows the LM5025 to operate a wide input voltage range (13 V – 100 V), benefiting customers by eliminating bias regulator components and reducing the printed board area.

National Semiconductor’s LM5025 PWM controller integrates a 100 V start-up bias regulator and a user programmable oscillator operating at 1 MHz, and exhibits total propagation delays of less than 100 nS, uniquely qualifying the device for a vast array of 48 V communication isolated power supply applications.  With the active clamp output, the LM5025 can be configured to provide either overlap time (for P-channel switch applications) or dead-off time (for N-channel switch applications).  National’s unique 3 A peak compound gate driver technology makes the LM5025 ideal for direct drive of a high-power MOSFET, reducing board space and leading to increased power density compared to alternative PWM controllers that require the addition of a gate driver chip.

Major features and benefits of National’s LM5025 are:

Features  Benefits
Integrated controller solution including Start-up regulator, high-frequency oscillator, control circuitry, and two power MOSFET drivers. Low component count. Reduced design time for an efficient forward with active clamp DC-DC converter.
Integrated dual 3 A and 1 A peak MOSFET gate drivers for main and clamp outputs. Improves efficiency and performance, eliminates need for external drivers.
Integrated wide range (15 V-to-100 V input) start-up regulator. Eliminates external start-up regulator components, enables users to operate power supply with a wide-range, unregulated input voltage.
Programmable dead-time or overlap time between main and clamp outputs. Drives either N-Channel or P-Channel active clamp transistor with user-defined timing of switch transitions.
User programmable under-voltage lockout (UVLO) circuitry with adjustable hysteresis. Flexibility to control power-ON sequencing and minimized start-up surge currents.
Dual-mode over-current protection.  Protects power supply with either cycle by cycle current limit or hiccup mode with soft-start. Protects against overload and short circuit.
Integrated oscillator synchronization circuitry. Allows users to reduce interference by locking the controller to an external clock.
Thermally enhanced, tiny (5 mm x 5 mm), LLP®-16 chip-scale package. Provides improved thermal performance.  Reduced overall PCB area.

“National’s LM5025 complements our industry-leading LM5000 family of high-voltage power ICs to offer no-compromise solutions to satisfy the escalating needs of our customers,” said Paul Greenland, marketing director of National Semiconductor’s power management group.  “The LM5025’s level of integration and functionality is superior to existing products, giving National a competitive edge in the fast growing distributed power supply market.”

Shipping now, the LM5025 is offered in a tiny LLP-16 or a TSSOP-16 package.  It is priced at $1.30 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, imaging sensors and data conversion solutions. National's key markets include wireless handsets, displays, PCs, networks and a broad range of portable applications. With headquarters in Santa Clara, California, National reported sales of $1.67 billion for fiscal 2003, which ended May 25, 2003. Additional company and product information is available at www.national.com