UC3845N

Product Summary

The UC3845N is a high performance fixed frequency current mode controller. It is specifically designed for Off-Line and dc-to-dc converter applications offering the designer a cost effective solution with minimal external components. The UC3845N features 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%. The UC3845N is available in an 8-pin dual-in-line 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 UC3845N has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off-line converters. It is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).

Parametrics

UC3845N absolute maximum ratings: (1)Total Power Supply and Zener Current (ICC + IZ): 30 mA; (2)Output Current, Source or Sink (Note 1) IO: 1.0 A; (3)Output Energy (Capacitive Load per Cycle) W: 5.0 μJ; (4)Current Sense and Voltage Feedback Inputs Vin: - 0.3 to + 5.5 V; (5)Error Amp Output Sink Current IO: 10 mA; (6)Power Dissipation and Thermal Characteristics N Suffix, Plastic Package, Case 626: Maximum Power Dissipation @ TA = 25℃ PD 1250 mW, Thermal Resistance Junction-to-Air RθJA 100℃/W; (7)Operating Junction Temperature TJ: + 150 ℃; (8)Operating Ambient Temperature TA: - 25 to + 85℃; (9)Storage Temperature Range Tstg: - 65 to + 150 ℃.

Features

UC3845N features: (1)Current Mode Operation to 500 kHz Output Switching Frequency; (2)Output Deadtime Adjustable from 50% to 70%; (3)Automatic Feed Forward Compensation; (4)Latching PWM for Cycle-By-Cycle Current Limiting; (5)Internally Trimmed Reference with Undervoltage Lockout; (6)High Current Totem Pole Output; (7)Input Undervoltage Lockout with Hysteresis; (8)Low Startup and Operating Current; (9)Direct Interface with ON Semiconductor SENSEFET Products.

Diagrams