1MHz PWM Controller IC Saves Components in Offline Supplies

The L4990 1MHz high speed Pulse Width Modulation (PWM) controller integrated circuit from SGS-THOMSON Microelectronics reduces the number of components in offline power supplies by integrating functions that competitors' circuits leave out. In addition to the essential current mode Pulse Width Modulation control circuits, it includes a hiccup mode pulse-by-pulse current limiter, overvoltage protection with shutdown, precise duty cycle control, programmable soft start, synchronization and internal 100ns leading edge blanking of current sense. All these features together save at least 20 external components, reducing board area, assembly and inventory costs.

Produced in mixed Bipolar-CMOS-DMOS (BCD) technology, the L4990 is a primary side controller IC that implements an offline or dc-dc converter supply using fixed frequency current mode control at switching frequencies up to 1MHz. It starts up with less than 0.5mA and has a high current output drive - up to 1A - suitable for power MOSFETs. Quiescent current is very low and a mixed bipolar-MOS driver circuit provides very high efficiency at high switching frequencies.

Applications where the L4990 will be useful include personal computers, monitors, servers, hubs and so on. It can be used both in ac-dc adapters and in dc-dc modules. Two versions of the circuit are offered with different undervoltage lockout limits. Each version is available in DIP16 and SO16W packages. An evaluation board is also available.

SGS-THOMSON's proprietary Multipower-BCD power technology family combines precise bipolar analog function, dense CMOS analog/digital control circuits and very efficient DMOS power stages on a single chip. Moreover, any number of power DMOS transistors can be integrated and because all contacts are on the top of the die they can be connected in any configuration. First developed in 1986, the technology has evolved to smaller lithographies and greater flexibility. The latest generation uses 1.2um lithography and allows even complex CMOS cells like microcomputer cores to be integrated with mixed power and signal circuits like those of the L4990.

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