PWM Controllers suit switch-mode power supplies.

Press Release Summary:

Soft-switching PWM controllers simplify implementation of active clamp/reset topologies and include auxiliary active clamp output driver. Peak current-mode units program critical delays to achieve proper active clamp operation and deliver zero-voltage switching to primary side MOSFET switches. Devices include internal programmable slope compensation circuit, maximum duty cycle limit, and 1 MHz synchronizable oscillator with internal timing capacitor.

Original Press Release:

TI Introduces New Active Clamp Soft-Switching PWM Controllers for High Efficiency Switch-Mode Power Supplies

Peak-Current Mode Controllers Minimize Power Loss, Lower EMI/RFI and Reduce Component Stresses for Higher Reliability

DALLAS (Dec. 11, 2003) - Texas Instruments Incorporated (TI) [NYSE: TXN announced today four new pulse-width modulation (PWM) controllers that significantly simplify implementation of active clamp/reset topologies for high-efficiency switching power supplies. The peak current-mode controllers increase efficiency in off-line power supplies and DC/DC converters used in high-end desktops, servers, 48-V telecommunications, data communications and 42-V automotive systems. See:

Ideal for active-clamp forward or flyback converters, TI's new UCC2891, UCC2892, UCC2893 and UCC2894 devices include an auxiliary active clamp output driver for efficient single-ended transformer reset. The controllers reduce switching losses of the converters by simply programming critical delays to achieve proper active clamp operation and deliver zero-voltage switching (ZVS) to the primary side MOSFET switches. Soft-switching allows the devices to achieve higher efficiencies at high operating frequencies, and increase reliability of the overall system by lowering electro-magnetic interference (EMI) and radio-frequency interference (RFI), and reducing power supply component losses.

Building upon the success of TI's first generation UCC3580 active-clamp controller, the four new controllers improve performance while eliminating many external components. The devices include an internal programmable slope compensation circuit, a precise maximum duty cycle limit and a 1-MHz synchronizable oscillator with an internal timing capacitor. For added performance and functionality, the devices feature programmable soft start and shutdown functionality and an accurate line monitoring function that can program a converter's on and off transitions when determining bulk input voltage levels. The UCC2891 and UCC2893 also feature a 110-V start-up feature that removes the need of an external trickle charge boot strap resistor to provide significant cost savings.

Key Features of the UCC2891, UCC2892, UCC2893 and UCC2894:

· Peak Current-Mode Control with Cycle-by-Cycle Current Limit

· Integrated ±2-A Gate Drivers with Programmable Turn-on Delay

· 110-V Internal Start-Up JFET Device in the UCC2891 and UCC2893

· 1MHz Oscillator with Programmable Maximum Duty Cycle Control

· Programmable Internal Slope Compensation

· Programmable Soft Start/Shutdown

· Accurate Line Under and Over-Voltage Sense Thresholds

Availability and Pricing

TI's UCC289x PWM controllers are available in volume from the company and its authorized distributors. Available in both 16-pin SOIC package and low-profile TSSOP packages, suggested resale pricing for the UCC2892 and UCC2894 is $1.49 in quantities of 1,000 units. Suggested resale pricing for the UCC2891 and UCC2893 with internal 110-V startup is $1.57 in quantities of 1,000 units. Evaluation modules of a 100-W 48-V to 3.3-V converter in half-brick format are available in less than 24 hours through

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