The UC3842B, UC3843B series are high performance fixed

frequency current mode controllers. They are specifically designed for

Off−Line and DC−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 (SOIC−8) 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 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).

Features

• 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

• This is a Pb−Free and Halide−Free Device