UC3845

Product Summary

The UC3845 is a high performance fixed frequency current mode controller. The device is specifically designed for Off-Line and dc-dc converter applications offering the designer a cost-effective solution with minimal external components. The UC3845 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. The UC3845 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 from 50% to 70%.

Parametrics

UC3845 absolute maximum ratings: (1)Total Power Supply and Zener Current, (ICC + IZ): 30 mA; (2)Output Current, Source or Sink, 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, D Suffix, Plastic Package, SOIC-14 Case 751A, Maximum Power Dissipation @ TA = 25℃, Thermal Resistance, Junction-to-Air, PD: 862mW, RθJA: 145℃/W; D1 Suffix, Plastic Package, SOIC-8 Case 751, Maximum Power Dissipation @ TA = 25℃, Thermal Resistance, Junction-to-Air, PD: 702mW, RθJA: 178℃/W; N Suffix, Plastic Package, Case 626, Maximum Power Dissipation @ TA = 25℃, Thermal Resistance, Junction-to-Air, PD: 1.25W, RθJA: 100℃/W; (7)Operating Junction Temperature, TJ: +150℃; (8)Operating Ambient Temperature, TA: 0 to + 70℃; (9)Storage Temperature Range, Tstg: -65 to +150℃.

Features

UC3845 features: (1)Pb-Free Packages are Available; (2)Trimmed Oscillator for Precise Frequency Control; (3)Oscillator Frequency Guaranteed at 250 kHz; (4)Current Mode Operation to 500 kHz Output Switching Frequency; (5)Output Deadtime Adjustable from 50% to 70%; (6)Automatic Feed Forward Compensation; (7)Latching PWM for Cycle-By-Cycle Current Limiting; (8)Internally Trimmed Reference with Undervoltage Lockout; (9)High Current Totem Pole Output; (10)Undervoltage Lockout with Hysteresis; (11)Low Startup and Operating Current.

Diagrams