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High Performance Current Mode Controllers

The UC3842B, UC3843B 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 a trimmed oscillator for precise duty cycle control, 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, programmable output deadtime, and a latch for single pulse metering. These devices are available in an 8–pin dual–in–line and surface mount (SO–8) plastic package as well as the 14–pin plastic surface mount (SO–14). The SO–14 package has separate power and ground pins for the totem pole output stage.

The UCX842B has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off–line converters. The UCX843B is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).

? Trimmed Oscillator for Precise Frequency Control

? Oscillator Frequency Guaranteed at 250 kHz

? Current Mode Operation to 500 kHz

? Automatic Feed Forward Compensation

? Latching PWM for Cycle–By–Cycle Current Limiting

? Internally Trimmed Reference with Undervoltage Lockout

? High Current Totem Pole Output

? Undervoltage Lockout with Hysteresis

? Low Startup and Operating Current