The UC3844B, UC3845B 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 deadtimes to be programmed from 50% to 70%.
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 UCX844B hasUVLO thresholds of 16 V (0n) and 10 V (off), ideally suited for
off-line converters. The UCX845B 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 at250 kHz
*Current Mode Operation to500 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
*Undervoltage Lockout with Hysteresis
*Low Startup and Operating Current
*Pb-Free Packages are Available