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Description The 3842A(AM)/43A(AM)/44A(AM)/45A(AM) are fixed frequency current mode PWM controller. They are specially designed for OFF-Line and DC to DC converter applications with a minimal external components. Internally implemented circuits include 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 circuitry includes built undervoltage lockout and current limiting. The 3842A(AM) and 3844A(AM) have UVLO thresholds of 16 V (on) and 10 V (off). The corresponding thresholds for the 3843A(AM)/45A(AM) are 8.4V (on) and 7.6V (off). The MIK3842A(AM) and MIK3843A(AM) can operate within 100% duty cycle. The 3844A(AM) and UC3845A(AM) can operate within 50% duty cycle. The 384XA(AM) has Start-Up Current 0.17mA (typ). Features * Low Start-Up and Operating Current * High Current Totem Pole Output * Undervoltage Lockout With Hysteresis * Operating Frequency Up To 300KHz (384XA) 500KHz (384XAM) Pin Connection Top view Block diagram (toggle flip flop used only in MIK3844, MIK3845) 7 V 8 5V VREF SET/ RESET UVLO VRE GOOD F LOGIC INTERNAL BIAS POWER VCC 7 1/2 VREF + 2 VFB ERR 1V 36V GND 5 2R C.S. COMP R PWM LATCH OUT 6 COMP 1 CURRENT SENSE 3 R S T R /C T 5 OSCILLATOR POWER GND Absolute Maximum Ratings Symbol VCC IO VI ISINK (E.A) Po Tstg TL Parameter Supply Voltage (low impedance source) Output Current Input Voltage (Analog Inputs pins 2,3) Error Amp Output Sink Current Power Dissipation (TA=250C) Storage Temperature Range Lead Temperature (soldering 5 sec.) Maximum 30 1 -0.3 to 5.5 10 1 -65 to150 260 Units V A V mA W o C o C BEIJING ESTEK ELECTRONICS CO.,LTD 1 Electrical characteristics (*VCC=15V, RT=10k, CT=3.3nF, TA=00C to +700C, unless otherwise specified) Characteristics 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 Supply Voltage Rejection Input Bias Current Output Section Low Output Voltage High Output Voltage Rise Time Fall Time Undervoltage Lockout Section Start Theshold Min. Operating Voltage (After Turn On) PWM Section Max. Duty Cycle Min. Duty Cycle Total Standby Current Start-Up Current D(MAX) D(MAX) IST MIK384XA(AM) 30 0.17 13 38 MIK3842A(AM)/43A(AM) MIK3844A(AM)/45A(AM) 95 47 97 48 100 50 0 0.3 17 % VTH(ST) VOPR(min) MIK3842A(AM)/44A(AM) MIK3843A(AM)/45A(AM) MIK3842A(AM)/44A(AM) MIK3843A(AM)/45A(AM) 14.5 7.8 8.5 7.0 16.0 8.4 10 7.6 17.5 9.0 11.5 8.2 V V f f/VCC V(OSC) IBIAS VI(E.A) AVOL PSRR ISINK ISOURCE VOH VOL GV VI(MAX) SVR IBIAS VOL VOH tR tF TJ = 25 C MIK384XA MIK384XAM 12V VCC 25 V (peak to peak) VFB=3V Vpin1 = 2.5V 2V V0 4V 12V VCC 25 V Vpin2 = 2.7V, Vpin1 = 1.1V Vpin2 = 2.3V, Vpin1 = 5V Vpin2 = 2.3V, RL = 15K to GND Vpin2 = 2.7V, RL = 15K to PIN 8 (Note 1 & 2) V pin1 = 5V (Note1) 12V VCC 25 V (Note 1) Vpin3 = 3V ISINK = 20 mA ISINK = 200 mA ISINK = 20 mA ISINK = 200 mA TJ = 25 CL = 1nF (Note 3) C, TJ = 25 CL = 1nF (Note 3) C, 13 12 2.85 0.9 47 47 50 52 0.05 1.6 -0.1 2.5 90 70 7 -1.0 6.0 0.8 3.0 1.0 70 -3.0 0.08 1.4 13.5 13.0 45 35 1.1 3.15 1.1 -10 0.4 2.2 V -2 2.58 57 57 1.0 KHz % V A V dB mA mA V VREF VREF VREF ISC TJ = 25 IREF = 1 mA C, 12V VCC 25 V 1 mA IREF 20mA TA = 25 C 4.9 5.0 6.0 6.0 -100 5.1 20 25 -180 mA V mV Symbol Test Conditions Min Typ Max Units 2.42 65 60 2 -0.5 5.0 V/V V dB A 150 150 nS Operating Supply Current ICC (OPR) Vpin3 = Vpin2 = 0V Zener Voltage VZ ICC=25 mA * - Adjust VCC above the start threshold before setting it to 15V. Note 1: Parameter measured at trip point of latch with Vpin2=0. Note 2: Gain defined as A=Vpin1/Vpin3 ; 0 Vpin3 0.8V. Note 3: These parameters, although guaranteed, are not 100% tested in production. mA V BEIJING ESTEK ELECTRONICS CO.,LTD 2 Pin functions N 1 2 3 4 5 6 7 8 Function COMP VFB ISENSE RT/CT GROUND OUTPUT VCC Vref Description This pin is the Error Amplifier output and is made for loop compensation. This is the inverting input of the Error Amplifier. It is normall y connected to the switching power supply output through a resistor divider. A voltage proportional to inductor current is connected to this input. The PWM uses this information to terminate the output switch conduction. The oscillator frequency and maximum Output duty cycle are programmed by connecting resistor R T to Vref and capacitor CT to ground. This pin is the combined control circuitry and power ground. This output directly drives the gate of a power MOSFET. Peak currents up to 1A are sourced and sink by this pin. This pin is the positive supply of the integrated circuit. This is the reference output. It provides charging current for capacitor C T through resistor RT . Application information 2.5V 1mA VFB COMP 2 1 Figure 1. Error Amp Configuration VCC 7 ON/OFF COMMAND TO S/R OF IC ICC MIK3842 MIK3843 MIK3844 MIK3845 13mA VON VOFF 16V 10V 8.4V 7.6V 0.2mA VCC VOFF VON During UVLO, the Output is low Figure 2. Undervoltage Lockout ERROR AMP + VFB 2 _ 2R 1V R CURRENT SENSE COMPARATOR COMP 1 IS R CURRENT SENSE 3 5 RS C GND Peak current is determined by IS max 1.0V RS Figure 3. Current Sense Circuit BEIJING ESTEK ELECTRONICS CO.,LTD 3 VREF RT RT /CT RSLOPE IS R1 RS ISENSE 8 VREF RT 8 4 RT /CT MIK3842 IS RSLOPE R1 5 4 MIK3842 3 ISENSE 3 5 GND RS GND Figure 4. Slope Compensation Techniques SCR must be selected for a holding current of less than 0.5mA. The simple two transistor circuit can be used in place of the SCR as shown. Figure 5. Latched Shutdown From V0 2.5 V RI Cf VFB 2 Rd Rf 1 COMP + - From V0 + 1mA EA R 2R Cp Cf Rp RI VFB 2.5 V + - + 1mA EA R 2R 2 Rf COMP 1 5 Error Amp compensation circuit for stabilizing any current-mode topology except for boost and flyback converters operating with continuous inductor current. Error Amp compensation circuit for stabilizing current-mode boost and flyback topologies operating with continuous inductor current. 5 Figure 6. Error Amplifier Compensation BEIJING ESTEK ELECTRONICS CO.,LTD 4 Figure 7. External Clock Synchronization Figure 8. Soft-Start Circuit BEIJING ESTEK ELECTRONICS CO.,LTD 5 Typical Performance Characteristics RT (K ) 50 % 50 C C 20 5nF 30 20 C 500pF C 1nF C 10nF 5nF C 2nF 10 10 C 200pF 5 C 10nF 5 C 3 100pF 2 1 10 500 VCC = 15 O 25 T C 20 30 50 100 200 300 2 VCC = T = 15 V O 25 f KHz) 1 10 500 20 30 50 100 200 300 f KHz) Figure 1. Timing Resistor vs. Oscillator Frequency. Dm ax (%) Figure 2. Output Dead-Time vs. Oscillator Frequenc . y (dB) 90 80 VCC = 15 V VO = 2V to 4V 100K R = L O 25 C 80 60 70 40 60 V = CC 15 V 3.3nF = 25 20 50 T 0 40 1 2 3 5 -20 Figure 3. Maximum Output Duty Cycle vs. Timing Resistor (MIK3842/4 3 .) Vth (V) 1.0 VCC = 15V R( T 10 100 1K 10K 100K 1M f (Hz) Figure 4. Error Amp Open-Loop Gain vs. Fr . equency IS C (mA) 100 VCC = 15 V 0.8 T O 90 25 C 0.6 T O 80 125 C 0.4 70 0.2 60 50 0 2 4 V ( O 0 25 50 75 100 O T ) Figure 5. Current Sense Input Threshold vs. Figure 6. Reference Short Circuit Current vs. Error Amp Output Voltage. Temperature. BEIJING ESTEK ELECTRONICS CO.,LTD 6 Vsat (V) -1 V 15 V ICC (m A) Sourse Saturation (Load to Ground) -2 80 s R ate Pulsed Load 120Hz 20 3 15 2 10 I = nse Se 0V 1 Sink Sa tura tion (Lo a d to 5 0V 10K R T = 25 A C 3.3nF C 0 0 Figure Current 0 200 400 600 I (m O 0 Figure . 8 Voltag . e 10 20 30 V ( CC . Output Saturation Voltage vs. Load 7 T 25 . Supply Current vs. Supply VCC Vref 8 PWM RT R C T 4 ID OUTPUT SMALL RT / LARGE 5 GND Figure 9. Oscillator and Output Waveforms 7 5V REG 6 OUTPUT R /C T OUTPUT CLOCK OSCILLATOR LARGE R / SMALL C T T / T R /C T T Ordering Information O RDERI NG NUM BER 3842 / 43 / 44/ 45 P ACK AG E SOP -8 / DI P - 8 6A06--6A07 Rm 6A07,Changyin Office Building ,No.88,Yong Ding Road,Hai Dian District ,Beijing Postalcode:100039 Tel: 86-010-58895780 / 81 / 82 / 83 / 84 Http://www.estek.com.cn Email:sales@estek.com.cn REV No:01-060815 BEIJING ESTEK ELECTRONICS CO.,LTD M AR K I NG KA3842/ 43 / 44/ 45 Address : Fax : 010-58895793 7 |
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