UC3842A

www.fairchildsemi.com UC3842A/UC3843A SMPS Controller Features Low Start Current 0.2mA (typ) Operating Range Up To 500KHz Cycle by Cycle Current Limiting Under Voltage Lock Out With Hysteresis Short Shutdown Delay Time: typ.100ns High Current Totem-pole Output Output Swing Limiting: 22V Description The UC3842A/UC3843A are fixed PWM controller for OffLine and DC to DC converter applications. The internal circuits include UVLO, low start up current circuit, temperature compensated reference, high gain error amplifier, current sensing comparator, and high current totem-pole output for driving a POWER MOSFET. Also UC3842A/ UC3843A provide low start up current below 0.3mA and short shutdown delay time typ. 100ns. The UC3842A has UVLO threshold of 16V(on) and 10V(off). The UC3843A is 8.4V(on) and 7.6V(off). The UC3842A and UC3843A can operate within 100% duty cycle. 8-DIP 1 8-SOP 1 Internal Block Diagram 7 VCC 29V VREF 8 Internal Bias 1/2VREF 5V VREF SET/ RESET UVLO 5 GND Good LOGIC 7 PWR VC VFB 2 Error Amp + - C.S PWM Comp. LATCH 1/3 1V S R 22V 6 OUTPUT COMP 1 5 PWR C.S 3 RT/CT 4 T GND OSCILLATOR Rev. 5.0 ©2000 Fairchild Semiconductor International UC3842A/UC3843A Absolute Maximum Ratings Parameter Supply Voltage Output Current Analog Inputs (pin 2, 3) Error Amp. Output Sink Current Power Dissipation Symbol VCC IO VI(ANA) ISINK(EA) PD Value 30 ±1 - 0.3 to 6.3 10 1 Unit V A V mA W Electrical Characteristics (VCC = 15V, RT = 10KΩ, CT = 3.3nF, ...