www.fairchildsemi.com KA3842B/KA3843B/KA3844B/KA3845B SMPS Controller Features Description * * * * The KA3842B/KA3843B/KA3844B/KA3845B are fixed frequency current-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 Ideally suited for driving a power MOSFET. Protection circuity Includes built in under-voltage lockout and current limiting. The KA3842B and KA3844B have UVLO thresholds of 16V (on) and 10V (off) The KA3843B and KA3845B are 8.5V (on) and 7.9V (off) The KA3842B and KA3843B can operate within 100% duty cycle. The KA3844B and KA3845B can operate with 50% duty cycle. Low Start Up Current Maximum Duty Clamp UVLO With Hysteresis Operating Frequency Up To 500KHz 8-DIP 1 14-SOP 1 Rev. 5.0 (c)2000 Fairchild Semiconductor International KA3842B/KA3843B/KA3844B/KA3845B Internal Block Diagram Absolute Maximum Ratings Parameter Supply Voltage Value Unit VCC 30 V IO 1 A V(ANA) -0.3 to 6.3 V Error Amp Output Sink Current ISINK (E.A) 10 mA Power Dissipation (TA = 25C) PD 1 W Output Current Analog Inputs (Pin 2.3) 2 Symbol KA3842B/KA3843B/KA3844B/KA3845B Electrical Characteristics (VCC=15V, RT=10K, CT=3.3nF, TA= 0C to +70C, unless otherwise specified) Parameter Symbol Conditions Min. Typ. Max. Unit 4.90 5.00 5.10 V 6 20 mV REFERENCE SECTION Reference Output Voltage VREF TJ = 25C, IREF = 1mA Line Regulation VREF 12VVCC25V - Load Regulation VREF Short Circuit Output Current 1mAIREF20mA - 6 25 mV ISC TA = 25C - -100 -180 mA f TJ = 25C 47 52 57 KHz 12VVCC25V - 0.05 1 % VOSC - - 1.6 - VP-P IBIAS - - -0.1 -2 A 2.42 2.50 2.58 V 2V VO 4V 65 90 - dB OSCILLATOR SECTION Oscillation Frequency Frequency Change with Voltage Oscillator Amplitude f/VCC ERROR AMPLIFIER SECTION Input Bias Current Input Voltage Open Loop Voltage Gain VI(E>A) GVO V1 = 2.5V Power Supply Rejection Ratio PSRR 12V VCC 25V 60 70 - dB Output Sink Current ISINK V2 = 2.7V, V1 = 1.1V 2 7 - mA -0.6 -1.0 - mA Output Source Current ISOURCE V2 = 2.3V, V1 = 5V High Output Voltage VOH V2 = 2.3V, RL = 15K to GND 5 6 - V Low Output Voltage VOL V2 = 2.7V, RL = 15K to Pin 8 - 0.8 1.1 V GV (Note 1 & 2) 2.85 3 3.15 V/V V1 = 5V(Note 1) 0.9 1 1.1 V - 70 - dB - -3 -10 A ISINK = 20mA - 0.08 0.4 V ISINK = 200mA - 1.4 2.2 V ISOURCE = 20mA 13 13.5 - V ISOURCE = 200mA 12 13.0 - V CURRENT SENSE SECTION Gain Maximum Input Signal VI(MAX) Power Supply Rejection Ratio PSRR Input Bias Current IBIAS 12V VCC 25V (Note 1) - OUTPUT SECTION Low Output Voltage High Output Voltage VOL VOH Rise Time tR TJ = 25C, CL= 1nF (Note 3) - 45 150 ns Fall Time tF TJ = 25C, CL= 1nF (Note 3) - 35 150 ns KA3842B/KA3844B 14.5 16.0 17.5 V KA3843B/KA3845B 7.8 8.4 9.0 V KA3842B/KA3844B 8.5 10.0 11.5 V KA3843B/KA3845B 7.0 7.6 8.2 V UNDER-VOLTAGE LOCKOUT SECTION Start Threshold Min. Operating Voltage (After Turn On) VTH(ST) VOPR(MIN) 3 KA3842B/KA3843B/KA3844B/KA3845B Electrical Characteristics (Continued) (VCC=15V, RT=10K, CT=3.3nF, TA= 0C to +70C unless otherwise specified) Parameter Symbol Conditions Min. Typ. Max. Unit PWM SECTION Max. Duty Cycle Min. Duty Cycle D(max) KA3842B/KA3843B 95 97 100 % D KA3844B/KA3845B 47 48 50 % D(MIN) - - - 0 % IST - - 0.45 1 mA TOTAL STANDBY CURRENT Start-Up Current Operating Supply Current Zener Voltage ICC(OPR) V3=V2=ON - 14 17 mA VZ ICC = 25mA 30 38 - V Adjust VCC above the start threshould before setting at 15V Note: 1. Parameter measured at trip point of latch 2. Gain defined as: V A = ----------1 ,0 V3 0.8V V 3 3.These parameters, although guaranteed, are not 100 tested in production. Figure 1. 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. The transistor and 5K potentiometer are used to sample the oscillator waveform and apply an adjustable ramp to pin 3. 4 KA3842B/KA3843B/KA3844B/KA3845B Figure 2. Under Voltage Lockout During Under-Voltage Lock-Out, the output driver is biased to a high impedance state. Pin 6 should be shunted to ground with a bleeder resistor to prevent activating the power switch with output leakage current. Figure 3. Error Amp Configuration Figure 4. Current Sense Circuit Peak current (IS) is determined by the formula: 1.0V I S ( MAX ) = -----------RS A small RC filter may be required to suppress switch transients. 5 KA3842B/KA3843B/KA3844B/KA3845B Figure 5. Oscillator Waveforms and Maximum Duty Cycle Oscillator timing capacitor, CT, is charged by VREF through RT, and discharged by an internal current source. During the discharge time, the internal clock signal blanks the output to the low state. Selection of RT and CT therefore determines both oscillator frequency and maximum duty cycle. Charge and discharge times are determined by the formulas: tc = 0.55 RT CT 0.0063R T - 2.7 t D = R T C T I n ---------------------------------------- 0.0063R T - 4 Frequency, then, is: f=(tc + td)-1 1.8 ForRT > 5K ,f = --------------RT CT Figure 6. Oscillator Dead Time & Frequency Figure 7. Timing Resistance vs Frequency (Deadtime vs CT RT > 5k) Figure 8. Shutdown Techniques 6 KA3842B/KA3843B/KA3844B/KA3845B Shutdown of the KA3842B can be accomplished by two methods; either raise pin 3 above 1V or pull pin 1 below a voltage two diode drops above ground. Either method causes the output of the PWM comparator to be high (refer to block diagram). The PWM latch is reset dominant so that the output will remain low until the next clock cycle after the shutdown condition at pins 1 and/or 3 is removed. In one example, an externally latched shutdown may be accomplished by adding an SOR which will be reset by cycling Voc below the lower UVLO threshold. At this point the reference turns off, allowing the SCR to reset. Figure 9. Slope Compensation A fraction of the oscillator ramp can be resistively summed with the current sense signal to provide slope compensation for converters requiring duty cycles over 50%. Note that capacitor, C, forms a filter with R2 to suppress the leading edge switch spikes. TEMPERATURE (C) TEMPERATURE (C) Figure 10. TEMPERATURE DRIFT (Vref) Figure 11. TEMPERATURE DRIFT (Ist) TEMPERATURE (C) Figure 12. TEMPERATURE DRIFT (Icc) 7 KA3842B/KA3843B/KA3844B/KA3845B Mechanical Dimensions Package 1.524 0.10 #5 2.54 0.100 5.08 MAX 0.200 7.62 0.300 3.40 0.20 0.134 0.008 +0.10 0.25 -0.05 +0.004 0~15 8 0.010 -0.002 3.30 0.30 0.130 0.012 0.33 0.013 MIN 0.060 0.004 #4 0.018 0.004 #8 9.60 MAX 0.378 #1 9.20 0.20 0.362 0.008 ( 6.40 0.20 0.252 0.008 0.46 0.10 0.79 ) 0.031 8-DIP KA3842B/KA3843B/KA3844B/KA3845B Mechanical Dimensions (Continued) Package 14-SOP MIN #8 0.60 0.20 0.024 0.008 MAX0.10 MAX0.004 1.80 MAX 0.071 5.72 0.225 8 3.95 0.20 0.156 0.008 0~ +0.10 0.20 -0.05 +0.004 0.008 -0.002 6.00 0.30 0.236 0.012 +0.10 0.406 -0.05 +0.004 0.016 -0.002 #7 1.27 0.050 #14 8.70 MAX 0.343 #1 8.56 0.20 0.337 0.008 ( 0.47 ) 0.019 1.55 0.10 0.061 0.004 0.05 0.002 9 KA3842B/KA3843B/KA3844B/KA3845B Ordering Information Product Number Package Operating Temperature KA3842B KA3843B KA3844B 8 DIP KA3845B 0 ~ + 70C KA3842BD KA3843BD KA3844BD KA3845BD 10 14 SOP KA3842B/KA3843B/KA3844B/KA3845B 11 KA3842B/KA3843B/KA3844B/KA3845B LIFE SUPPORT POLICY FAIRCHILD'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR INTERNATIONAL. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user. 2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com 7/13/00 0.0m 001 Stock#DSxxxxxxxx 2000 Fairchild Semiconductor International