Dallas - Texas Instruments' newest generation of pulse-width modulation (PWM) controllers, the UCC2891 through UCC2894, are designed to significantly simplify implementation of active clamp/reset and synchronous rectifier 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-volt telecommunications, data communications and 42-volt automotive systems.
Suited to active-clamp forward or flyback converter topologies that are key to high-efficiency, zero voltage switching (ZVS) designs, these devices include an auxiliary active-clamp output driver for single-ended transformer reset. They also contain the logic for simply programming the 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 ultimately increases reliability of the overall system by reducing EMI and RFI.
TI says the four new controllers improve performance of its first generation UCC3580 devices 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 as the controller determines bulk input voltage levels. The UCC2891 and UCC2893 also feature a 110-V start-up feature that removes the need for an external trickle-charge bootstrap resistor.
The UCC289x PWM controllers are available in volume. Available in both 16-pin SOIC package and low-profile TSSOP packages, they are suggested resale priced at $1.49 for the UCC2892 and UCC2894 and $1.57 for the UCC2891 and UCC2893, all in 1k units. Evaluation modules of a 100-watt 48- to 3.3-volt converter in half-brick format are available in less than 24 hours.