UC2843B

UMW R UMW UC2842/43/44/45 Description The 2842/43/44/45 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 2842 and 2844 have UVLO thresholds of 16V (on) and 10V (off). The corresponding thresholds for the 2843/ 45 are 8.4V (on) and 7.6V (off). The 2842 and 2843 can operate within 100% duty cycle. The 2844 and 2845 can operate within 50% duty cycle. The 284X has Start-Up Current 0.5mA (typ). Pin Connection Features • • • • Low Start-Up and Operating Current High Current Totem Pole Output Undervoltage Lockout With Hysteresis Operating Frequency Up To 500KHz Top view Block diagram (toggle flip flop used only in 2844, 2845) V R T Absolute Maximum Ratings Symbol VCC Parameter Maximum Units Supply Voltage (low impedance source) 30 V IO Output Current ±1 A VI Input Voltage (Analog Inputs pins 2,3) −0.3 to 5.5 V Error Amp Output Sink Current Power Dissipation (TA=250C) Storage Temperature Range 10 1 -65 to150 mA W o C ISINK (E.A) Po Tstg TL TA Lead Temperature (soldering 5 sec.) Operating Ambient Temperature www.umw-ic.com 1 260 o -25 to +85 o C C 友台半导体有限公司 UMW R UMW UC2842/43/44/45 Electrical characteristics (*VCC=15V, RT=10kΩ, CT=3.3nF, TA=00C to +700C, unless otherwise specified) Characteristics Symbol Test Conditions Min Typ Max Units 4.9 5.0 5.1 V mV Reference Section Reference Output Voltage VREF TJ = 25°C, IREF = 1 mA Line Regulation ∆VREF 12V ≤ VCC ≤ 25 V 6.0 20 Load Regulation ∆VREF 1 mA ≤ IREF ≤ 20mA 6.0 25 -100 -180 Short Circuit Output Current ISC TA = 25°C f TJ = 25°C mA Oscillator Section Oscillation Frequency ∆f/∆VCC 284X 47 50 57 284X 47 52 57 1.0 12V ≤ VCC ≤ 25 V 0.05 Oscillator Amplitude Error Amplifier Section V(OSC) (peak to peak) 1.6 Input Bias Current Input Voltage Open Loop Voltage Gain Power Supply Rejection Ratio IBIAS VI(E.A) AVOL PSRR VFB=3V Vpin1 = 2.5V 2V ≤ V0 ≤ 4V 12V ≤ VCC ≤ 25 V Frequency Change with Voltage Output Sink Current Output Source Current ISINK ISOURCE Vpin2 = 2.7V, Vpin1 = 1.1V -2 2.58 dB 7 mA -1.0 mA 5.0 6.0 VOH Vpin2 = 2.3V, RL = 15KΩ to GND Vpin2 = 2.7V, RL = 15KΩ to PIN 8 GV (Note 1 & 2) V pin1 = 5V (Note1) 12V ≤ VCC ≤ 25 V (Note 1) V 0.8 1.1 2.85 3.0 3.15 V/V 0.9 1.0 70 1.1 V dB µA Input Bias Current Output Section IBIAS Vpin3 = 3V -3.0 -10 Low Output Voltage VOL ISINK = 20 mA 0.08 0.4 1.4 13.5 13.0 2.2 VOH ISINK = 200 mA ISINK = 20 mA ISINK = 200 mA High Output Voltage µA V 2 VOL VI(MAX) SVR V -0.5 High Output Voltage Maximum Input Signal Supply Voltage Rejection -0.1 2.5 90 70 % Vpin2 = 2.3V, Vpin1 = 5V Low Output Voltage Current Sense Section Gain 2.42 65 60 KHz 13 12 Rise Time tR TJ = 25°C, CL = 1nF (Note 3) 45 150 Fall Time tF TJ = 25°C, CL = 1nF (Note 3) 35 150 V nS Undervoltage Lockout Section Start Theshold Min. Operating Voltage (After Turn On) VTH(ST) 2842/44 14.5 16.0 17.5 VOPR(min) 2843/45 2842/44 7.8 8.5 8.4 10 9.0 11.5 2843/45 7.0 7.6 8.2 2842/43 2844/45 95 47 97 100 48 50 V V PWM Section Max. Duty Cycle Min. Duty Cycle Total Standby Current Start−Up Current D(MAX) D(MAX) IST 284X 0.5 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. www.umw-ic.com % 0 2 30 13 38 mA 17 V 友台半导体有限公司 UMW R UMW UC2842/43/44/45 Pin functions 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 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 2 COMP 1 Figure 1. Error Amp Configuration VCC 7 ON/OFF COMMAND TO S/R OF IC ICC 2842 2844 2843 2845 VON 16V 8.4V VOFF 10V 7.6V 13mA 0.2mA VCC VOFF VON During UVLO, the Output is low Figure 2. Undervoltage Lockout + VFB ERROR AMP 2 _ 2R 1V COMP 1 R IS CURRENT SENSE COMPARATOR R CURRENT SENSE RS C 3 5 GND Peak current is determined by IS max 1.0V RS Figure 3. Current Sense Circuit www.umw-ic.com 3 友台半导体有限公司 R UMW UMW UC2842/43/44/45 VREF VREF 8 RT 8 RT RT /CT 4 RSLOPE RT /CT 2842 RSLOPE IS 4 2842 IS R1 ISENSE R1 3 5 RS ISENSE 3 5 RS GND 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 From V0 + 2.5 V RI + VFB 2 Rd Cf 1mA - Rf 2R RI EA - 2 Cf 1 1mA + VFB Cp R + 2.5 V Rp Rf 2R EA R COMP 1 COMP 5 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. Figure 6. Error Amplifier Compensation www.umw-ic.com 4 友台半导体有限公司 UMW R UMW UC2842/43/44/45 Figure 7. External Clock Synchronization Figure 8. Soft-Start Circuit www.umw-ic.com 5 友台半导体有限公司 UMW R UMW UC2842/43/44/45 Typical Performance Characteristics )Ω C 500 500 Figure 1. Timing Resistor vs. Oscillator Frequency Figure 2. Output Dead-Time vs. Oscillator Frequency Figure 3. Maximum Output Duty Cycle vs. Timing Resistor (UC3842/43) Figure 4. Error Amp Open-Loop Gain vs. Frequency Figure 5. Current Sense Input Threshold vs. Error Amp Output Voltage www.umw-ic.com Figure 6. Reference Short Circuit Current vs. Temperature 6 友台半导体有限公司 ., UMW R UMW UC2842/43/44/45 Rate C Figure 7. Output Saturation Voltage vs. Load Current Current TA = 25°C 5 . Figure 8. Supply Current vs. Supply Voltage o tag .e Figure 9. Oscillator and Output Waveforms www.umw-ic.com 7 友台半导体有限公司 UMW R UMW UC2842/43/44/45 SOP-8 Symbol A A1 A2 b c D E E1 e L θ www.umw-ic.com Dimensions In Millimeters Min Max 1.350 1.750 0.100 0.250 1.350 1.550 0.330 0.510 0.170 0.250 4.700 5.100 3.800 4.000 5.800 6.200 1.270(BSC) 0.400 1.270 0° 8° 8 Dimensions In Inches Min Max 0.053 0.069 0.004 0.010 0.053 0.061 0.013 0.020 0.006 0.010 0.185 0.200 0.150 0.157 0.228 0.244 0.050(BSC) 0.016 0.050 0° 8° 友台半导体有限公司 UMW R UMW UC2842/43/44/45 Ordering information Order code Package Baseqty Deliverymode UMW UC2842B SOP-8 2500 Tape and reel UMW UC2843B SOP-8 2500 Tape and reel UMW UC2844B SOP-8 2500 Tape and reel UMW UC2845B SOP-8 2500 Tape and reel www.umw-ic.com 9 友台半导体有限公司