Current Mode PWM Controller KA3843A(AM) DESCRIPTION The KA3843AM 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 corresponding thresholds for the The KA3843AM are 8.4V(on) and 7.6V (off) The KA3843AM can operate within 100% duty cycle. The KA3843AM 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 500KHz BLOCK DIAGRAM Absolute Maximum Ratings Characteristic Supply Voltage (low impedance source) Output Current Symbol VCC Value 30 Unit V IO ±1 A Input Voltage (Analog Inputs pins 2,3) VI Error Amp Output Sink Current Power Dissipation (TA=250C) Storage Temperature Range Lead Temperature (soldering 5 sec.) ISINK (E.A) PO Tstg TL −0.3 to 5.5 10 1 -65 to150 260 mA W oC oC 1 V PIN CONNECTION (TOP VIEW) Current Mode PWM Controller KA3843A(AM) Electrical characteristics (*VCC=15V, RT=10kΩ, CT=3.3nF, TA=00C to +700C, unless otherwise specified) Characteristics Symbol Test Condition Min Typ Max Reference Section Reference Output Voltage VREF 5.0 5.1 V Line Regulation ∆VREF 12V ≤ VCC ≤ 25 V 6.0 20 mV Load Regulation ∆VREF ISC 1 mA ≤ IREF ≤ 20mA 6.0 25 TA = 25°C -100 -180 f TJ = 25°C 50 52 0.05 57 57 1.0 Short Circuit Output Current TJ = 25°C, IREF = 1 mA 4.9 Unit mA Oscillator Section Oscillation Frequency Frequency Change with Voltage Oscillator Amplitude Error Amplifier Section Input Bias Current ∆f/∆VCC Input Voltage Open Loop Voltage Gain VI(E.A) AVOL Power Supply Rejection Ratio PSRR Output Sink Current Output Source Current High Output Voltage Low Output Voltage Current Sense Section Gain Maximum Input Signal Supply Voltage Rejection V(OSC) IBIAS ISINK ISOURCE VOH VOL GV VI(MAX) SVR Input Bias Current IBIAS Output Section Low Output Voltage VOL High Output Voltage VOH Rise Time tR Fall Time tF 384XA 384XAM 47 47 12V ≤ VCC ≤ 25 V (peak to peak) 1.6 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 = 15KΩ to GND -0.1 -2 2.42 65 2.5 90 2.58 60 70 2 -0.5 5.0 7 -1.0 6.0 µA V dB mA mA V 0.8 1.1 3.0 1.0 70 3.15 1.1 V/V V dB -3.0 -10 µA 0.4 2.2 TJ = 25°C, CL = 1nF (Note 3) 0.08 1.4 13.5 13.0 45 150 TJ = 25°C, CL = 1nF (Note 3) 35 150 Vpin2 = 2.7V, RL = 15KΩ to PIN 8 (Note 1 & 2) V pin1 = 5V (Note1) 2.85 0.9 12V ≤ VCC ≤ 25 V (Note 1) Vpin3 = 3V ISINK ISINK ISINK ISINK = = = = 20 mA 200 mA 20 mA 200 mA 13 12 3843A(AM) 7.8 8.4 9.0 3843A(AM)/45A(AM) 7.0 7.6 8.2 95 97 VOPR(min) D (MAX) % V Undervoltage Lockout Section Start Theshold VTH(ST) Min. Operating Voltage (After Turn On) PWM Section Max. Duty Cycle KHz 3842A(AM)/43A(AM) V nS V V 100 % Min. Duty Cycle Total Standby Current D(MAX) 0 384XA(AM) IST Start−Up Current Operating Supply Current ICC (OPR) Vpin3 = Vpin2 = 0V Zener Voltage VZ ICC=25 mA 30 * 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. 2 0.17 0.3 13 38 17 mA V Current Mode PWM Controller KA3843A(AM) PIN FUNCTION N 1 2 FUNCTION COMP VFB 3 ISENSE 4 RT/CT 5 6 GROUND OUTPUT 7 8 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 normally 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 RT 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 CT through resistor RT . APPLICATION INFORMATION Figure 1. Error Amp Configuration WS WS Figure 2. Undervoltage Lockout 3 Current Mode PWM Controller KA3843A(AM) Figure 3. Current Sense Circuit Figure 4. Slope Compensation Techniques 4 Current Mode PWM Controller KA3843A(AM) 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 Figure 6. Error Amplifier Compensation 5 Current Mode PWM Controller KA3843A(AM) Figure 7. External Clock Synchronization Figure 8. Soft-Start Circuit 6 Current Mode PWM Controller KA3843A(AM) TYPICAL PERFORMANCE CHARACTERISTICS Figure 1. Timing Resistor vs. Oscillator Frequency Figure 2. Output Dead-Time vs. Oscillator Frequency Figure 3. Maximum Output Duty Cycle vs. Timing Resistor (3842/43) Figure 4. Error Amp Open-Loop Gain vs. Frequency Figure 5. Current Sense Input Threshold vs. Error Amp Output Voltage Figure 6. Reference Short Circuit Current vs. Temperature 7 Current Mode PWM Controller KA3843A(AM) Figure 7. Output Saturation Voltage vs. Load Current TA = 25°C Figure 8. Supply Current vs. Supply Voltage Figure 9. Oscillator and Output Waveforms 8 Current Mode PWM Controller KA3843A(AM) PAD LOCATION Chip size: 2.38 x 1.63 mm Pad N Pad Name 1 2 3 4 5 6 7 8 9 10 COMP VFB ISENSE RT/CT POWER GND GND OUT POWER VCC VCC VREF Coordinates µm X Y 90 110 1050 110 1310 110 2000 150 1700 1280 1680 1450 1310 1410 990 1410 815 1410 460 1390 9