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www.fairchildsemi.com UC3842/UC3843/UC3844/UC3845 SMPS Controller Features · · · · Low Start up Current Maximum Duty Clamp UVLO With Hysteresis Operating Frequency up to 500KHz Description The UC3842/UC3843/UC3844/UC3845 are fixed frequencycurrent-mode PWM controller. They are specially designed for Off-Line and DC to DC converter applications with minimum 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 totempole output for driving a Power MOSFET. The UC3842 and UC3844 have UVLO thresholds of 16V (on) and 10V (off). The UC3843 and UC3845 are 8.5V(on) and 7.9V (off). The UC3842 and UC3843 can operate within 100% duty cycle. The UC3844 and UC3845 can operate with 50% duty cycle. 8-DIP 8-SOP 1 1 14-SOP 1 Internal Block Diagram * NORMALLY 8DIP/8SOP PIN NO. * ( ) IS 14SOP PINNO. * TOGGLE FLIP FLOP USED ONLY IN UC3844, UC3845 Rev. 1.0.1 ©2002 Fairchild Semiconductor Corporation UC3842/UC3843/UC3844/UC3845 Absolute Maximum Ratings Parameter Supply Voltage Output Current Analog Inputs (Pin 2.3) Error Amp Output Sink Current Power Dissipation at TA25°C (8DIP) Power Dissipation at TA25°C (8SOP) Power Dissipation at TA25°C (14SOP) Storage Temperature Range Lead Temperature (Soldering, 10sec) Symbol VCC IO V(ANA) ISINK (E.A) PD(Note1,2) PD(Note1,2) PD(Note1,2) TSTG TLEAD Value 30 ±1 -0.3 to 6.3 10 1200 460 680 -65 ~ +150 +300 Unit V A V mA mW mW mW °C °C Note: 1. Board Thickness 1.6mm, Board Dimension 76.2mm Ч114.3mm, (Reference EIA / JSED51-3, 51-7) 2. Do not exceeed PD and SOA (Safe Operation Area) Power Dissipation Curve 1200 8DIP 1100 POWER DISSIPATION (mW) 1000 900 800 700 600 500 400 300 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 14SOP 8SOP AMBIENT TEMPERATURE () Thermal Data Characteristic Thermal Resistance Junction-ambient Symbol Rthj-amb(MAX) 8-DIP 100 8-SOP 265 14-SOP 180 Unit °C/W Pin Array 8DIP,8SOP 14SOP COMP 1 8 VREF COMP 1 14 VREF VFB 2 7 VCC N/C 2 13 N/C CURRENT SENSE 3 6 OUTPUT VFB 3 12 VCC RT/ CT 4 5 GND N/C 4 11 PWR VC CURRENT SENSE 5 10 OUTPUT N/C 6 9 GND RT/C T 7 8 PWR GND 2 UC3842/UC3843/UC3844/UC3845 Electrical Characteristics (VCC=15V, RT=10k, CT=3.3nF, TA= 0°C to +70°C, unless otherwise specified) Parameter REFERENCE SECTION Reference Output Voltage Line Regulation Load Regulation Short Circuit Output Current OSCILLATOR SECTION Oscillation Frequency Frequency Change with Voltage Oscillator Amplitude ERROR AMPLIFIER SECTION Input Bias Current Input Voltage Open Loop Voltage Gain Power Supply Rejection Ratio Output Sink Current Output Source Current High Output Voltage Low Output Voltage CURRENT SENSE SECTION Gain Maximum Input Signal Power Supply Rejection Ratio Input Bias Current OUTPUT SECTION Low Output Voltage High Output Voltage Rise Time Fall Time Start Threshold Min. Operating Voltage (After Turn