The UC3844, UC3845 series are high performance fixed frequency current mode controllers. They are specifically designed for Off?Line and DC?to?DC converter applications offering the designer a cost effective solution with minimal external components. These integrated circuits feature an oscillator, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totem pole output ideally suited for driving a power MOSFET.

Also included are protective features consisting of input and reference undervoltage lockouts each with hysteresis, cycle?by?cycle current limiting, a latch for single pulse metering, and a flip?flop which blanks the output off every other oscillator cycle, allowing output dead times to be programmed for 50 to 70.

These devices are available in an 8?pin dual?in?line plastic package as well as the 14?pin plastic surface mount (SOIC?14). The SOIC?14 package has separate power and ground pins for the totem pole output stage.

The UCX844 has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off?line converters. The UCX845 is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).

Features

? Current Mode Operation to 500 kHz Output Switching Frequency

? Output Deadtime Adjustable from 50 to 70

? Automatic Feed Forward Compensation

? Latching PWM for Cycle?By?Cycle Current Limiting

? Internally Trimmed Reference with Undervoltage Lockout

? High Current Totem Pole Output

? Input Undervoltage Lockout with Hysteresis

? Low Startup and Operating Current

? Direct Interface with ON Semiconductor SENSEFET? Products

? Pb?Free Packages are Available