![]() ![]() Under Voltage Lockout During Under-Voltage Lock-Out, the output driver is biased to a high impedance state. The transistor and 5kΩ potentiometer are used to sample the oscillator waveform and apply an adjustable ramp to pin 3. ![]() Open Loop Test Circuit High peak currents associated with capacitive loads necessitate careful grounding techniques Timing and bypass capacitors should be connected close to pin 5 in a single point ground. ![]() These parameters, although guaranteed, are not 100 tested in production. Gain defined as: V A = pin1,0 Vpin3 0.8V V pin3 3. Parameter measured at trip point of latch 2. Duty Cycle D(MIN) % TOTAL STANDBY CURRENT Start-Up Current IST ma Operating Supply Current ICC(OPR) Vpin3=Vpin2=ON ma Zener Voltage VZ ICC = 25mA V Adjust VCC above the start threshould before setting at 15V Note: 1. Operating Voltage UC3842/UC V VOPR(MIN) (After Turn On) UC3843/UC V 3Ĥ UC3842/UC3843/UC3844/UC3845 Electrical Characteristics (Continued) (VCC=15V, RT=10kΩ, CT=3.3nF, TA= 0 C to +70 C, unless otherwise specified) Parameter Symbol Conditions Min. Unit REFERENCE SECTION Reference Output Voltage VREF TJ = 25 C, IREF = 1mA V Line Regulation VREF 12V VCC 25V mv Load Regulation VREF 1mA IREF 20mA mv Short Circuit Output Current ISC TA = 25 C ma OSCILLATOR SECTION Oscillation Frequency f TJ = 25 C khz Frequency Change with Voltage f/ VCC 12V VCC 25V % Oscillator Amplitude VOSC VP-P ERROR AMPLIFIER SECTION Input Bias Current IBIAS µa Input Voltage VI(E>A) Vpin1 = 2.5V V Open Loop Voltage Gain GVO 2V VO 4V (Note3) db Power Supply Rejection Ratio PSRR 12V VCC 25V (Note3) db Output Sink Current ISINK Vpin2 = 2.7V, Vpin1 = 1.1V ma Output Source Current ISOURCE Vpin2 = 2.3V, Vpin1 = 5V ma High Output Voltage VOH Vpin2 = 2.3V, RL = 15kΩ to GND V Low Output Voltage VOL Vpin2 = 2.7V, RL = 15kΩ to Pin V CURRENT SENSE SECTION Gain GV (Note 1 & 2) V/V Maximum Input Signal VI(MAX) Vpin1 = 5V(Note 1) V Power Supply Rejection Ratio PSRR 12V VCC 25V (Note 1,3) db Input Bias Current IBIAS µa OUTPUT SECTION Low Output Voltage VOL ISINK = 20mA V ISINK = 200mA V High Output Voltage ISOURCE = 20mA V VOH ISOURCE = 200mA V Rise Time tr TJ = 25 C, CL= 1nF (Note 3) ns Fall Time tf TJ = 25 C, CL= 1nF (Note 3) ns UNDER-VOLTAGE LOCKOUT SECTION Start Threshold UC3842/UC V VTH(ST) UC3843/UC V Min. Do not exceeed PD and SOA (Safe Operation Area) Power Dissipation Curve POWER DISSIPATION (mw) DIP 14SOP 8SOP AMBIENT TEMPERATURE ( ) Thermal Data Characteristic Symbol 8-DIP 8-SOP 14-SOP Unit Thermal Resistance Junction-ambient Rthj-amb(MAX) 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/CT 7 8 PWR GND 2ģ UC3842/UC3843/UC3844/UC3845 Electrical Characteristics (VCC=15V, RT=10kΩ, CT=3.3nF, TA= 0 C to +70 C, unless otherwise specified) Parameter Symbol Conditions Min. Board Thickness 1.6mm, Board Dimension 76.2mm 114.3mm, (Reference EIA / JSED51-3, 51-7) 2. * TOGGLE FLIP FLOP USED ONLY IN UC3844, UC3845 Rev Fairchild Semiconductor CorporationĢ UC3842/UC3843/UC3844/UC3845 Absolute Maximum Ratings Parameter Symbol Value Unit Supply Voltage VCC 30 V Output Current IO ☑ A Analog Inputs (Pin 2.3) V(ANA) -0.3 to 6.3 V Error Amp Output Sink Current ISINK (E.A) 10 ma Power Dissipation at TA 25 C (8DIP) PD(Note1,2) 1200 mw Power Dissipation at TA 25 C (8SOP) PD(Note1,2) 460 mw Power Dissipation at TA 25 C (14SOP) PD(Note1,2) 680 mw Storage Temperature Range TSTG -65 ~ +150 C Lead Temperature (Soldering, 10sec) TLEAD +300 C Note: 1. 8-DIP 8-SOP 1 14-SOP 1 1 Internal Block Diagram * NORMALLY 8DIP/8SOP PIN NO. The UC3844 and UC3845 can operate with 50% duty cycle. The UC3842 and UC3843 can operate within 100% duty cycle. ![]() The UC3842 and UC3844 have UVLO thresholds of 16V (on) and 10V (off). 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. They are specially designed for Off-Line and DC to DC converter applications with minimum external components. 1 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. ![]()
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