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