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| www.fairchildsemi.com KA3842B/KA3843B/KA3844B/KA3845B SMPS Controller Features * * * * Low Start Up Current Maximum Duty Clamp UVLO With Hysteresis Operating Frequency Up To 500KHz 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. 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 Output Current Analog Inputs (Pin 2.3) Error Amp Output Sink Current Power Dissipation (TA = 25C) Symbol VCC IO V(ANA) ISINK (E.A) PD Value 30 1 -0.3 to 6.3 10 1 Unit V A V mA W 2 KA3842B/KA3843B/KA3844B/KA3845B Electrical Characteristics (VCC=15V, RT=10K, CT=3.3nF, TA= 0C to +70C, 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 On) VOL ISINK = 20mA ISINK = 200mA VOH tR tF ISOURCE = 20mA ISOURCE = 200mA TJ = 25C, CL= 1nF (Note 3) TJ = 25C, CL= 1nF (Note 3) KA3842B/KA3844B KA3843B/KA3845B KA3842B/KA3844B KA3843B/KA3845B 13 12 14.5 7.8 8.5 7.0 0.08 1.4 13.5 13.0 45 35 16.0 8.4 10.0 7.6 0.4 2.2 150 150 17.5 9.0 11.5 8.2 V V V V ns ns V V V V GV VI(MAX) PSRR IBIAS (Note 1 & 2) V1 = 5V(Note 1) 12V VCC 25V (Note 1) 2.85 0.9 3 1 70 -3 3.15 1.1 -10 V/V V dB A IBIAS VI(E>A) GVO PSRR ISINK ISOURCE VOH VOL V1 = 2.5V 2V VO 4V 12V VCC 25V V2 = 2.7V, V1 = 1.1V V2 = 2.3V, V1 = 5V V2 = 2.3V, RL = 15K to GND V2 = 2.7V, RL = 15K to Pin 8 2.42 65 60 2 -0.6 5 -0.1 2.50 90 70 7 -1.0 6 0.8 -2 2.58 1.1 A V dB dB mA mA V V f f/VCC VOSC TJ = 25C 12VVCC25V 47 52 0.05 1.6 57 1 KHz % VP-P VREF VREF VREF ISC TJ = 25C, IREF = 1mA 12VVCC25V 1mAIREF20mA TA = 25C 4.90 5.00 6 6 -100 5.10 20 25 -180 V mV mV mA Symbol Conditions Min. Typ. Max. Unit UNDER-VOLTAGE LOCKOUT SECTION 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 PWM SECTION Max. Duty Cycle Min. Duty Cycle TOTAL STANDBY CURRENT Start-Up Current Operating Supply Current Zener Voltage IST ICC(OPR) VZ V3=V2=ON ICC = 25mA 30 0.45 14 38 1 17 mA mA V D(max) D D(MIN) KA3842B/KA3843B KA3844B/KA3845B 95 47 97 48 100 50 0 % % % Symbol Conditions Min. Typ. Max. Unit Adjust VCC above the start threshould before setting at 15V Note: 1. Parameter measured at trip point of latch 2. Gain defined as: V 1 A = ---------,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) Figure 10. TEMPERATURE DRIFT (Vref) TEMPERATURE (C) Figure 11. TEMPERATURE DRIFT (Ist) TEMPERATURE (C) Figure 12. TEMPERATURE DRIFT (Icc) 7 KA3842B/KA3843B/KA3844B/KA3845B Mechanical Dimensions Package 8-DIP 6.40 0.20 0.252 0.008 0.79 ) 0.031 1.524 0.10 #1 #8 #4 #5 9.20 0.20 0.362 0.008 9.60 MAX 0.378 5.08 MAX 0.200 7.62 0.300 3.40 0.20 0.134 0.008 3.30 0.30 0.130 0.012 0.33 0.013 MIN 0.25 -0.05 +0.10 0~15 0.010 -0.002 +0.004 8 2.54 0.100 0.018 0.004 0.060 0.004 0.46 0.10 ( KA3842B/KA3843B/KA3844B/KA3845B Mechanical Dimensions (Continued) Package 14-SOP MIN 1.55 0.10 0.061 0.004 0.05 0.002 #1 #14 8.70 MAX 0.343 8.56 0.20 0.337 0.008 #7 6.00 0.30 0.236 0.012 #8 1.80 MAX 0.071 +0.10 0.20 -0.05 +0.004 0.008 -0.002 3.95 0.20 0.156 0.008 0.60 0.20 0.024 0.008 5.72 0.225 0~ 8 MAX0.10 MAX0.004 1.27 0.050 +0.10 0.406 -0.05 +0.004 0.016 -0.002 ( 0.47 ) 0.019 9 KA3842B/KA3843B/KA3844B/KA3845B Ordering Information Product Number KA3842B KA3843B KA3844B KA3845B KA3842BD KA3843BD KA3844BD KA3845BD 14 SOP 8 DIP 0 ~ + 70C Package Operating Temperature 10 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. www.fairchildsemi.com 7/13/00 0.0m 001 Stock#DSxxxxxxxx 2000 Fairchild Semiconductor International 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. |
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