UC3843B

UMW R UMW UC3842/43/44/45 Description The 3842/43/44/45 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 3842 and 3844 have UVLO thresholds of 16 V (on) and 10 V (off). The corresponding thresholds for the 3843/ 45 are 8.4V (on) and 7.6V (off). The 3842) and 3843 can operate within 100% duty cycle. The 3844 and 3845 can operate within 50% duty cycle. The 384X has Start-Up Current 0.17mA (typ). Pin Connection Features • Low Start-Up and Operating Current • High Current Totem Pole Output • Undervoltage Lockout With Hysteresis •Operating Frequency Up To 300KHz (384X) 500KHz (384X) Top view Block diagram (toggle flip flop used only in 3844, 3845) 7 5V VREF V 8 36V SET/ RESET GND 5 UVLO VRE GOOD F LOGIC INTERNAL BIAS POWER VCC 7 1/2 VREF 2R + 2 VFB ERR C.S. COMP 1V R R COMP OUT PWM LATCH 6 1 CURRENT SENSE S 3 T R /C T 5 OSCILLATOR POWER GND 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 Lead Temperature (soldering 5 sec.) www.umw-ic.com 260 1 o C 友台半导体有限公司 UMW R UMW UC3842/43/44/45 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 384X 47 50 57 384X 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 -0.1 2.5 90 70 -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 % Vpin2 = 2.3V, Vpin1 = 5V Low Output Voltage Current Sense Section Gain 2.42 65 60 KHz 13 12 V Rise Time tR TJ = 25°C, CL = 1nF (Note 3) 45 150 Fall Time tF TJ = 25°C, CL = 1nF (Note 3) 35 150 nS Undervoltage Lockout Section Start Theshold Min. Operating Voltage (After Turn On) VTH(ST) 3842/44 14.5 16.0 17.5 VOPR(min) 3843/45 3842/44 7.8 8.5 8.4 10 9.0 11.5 3843/45 7.0 7.6 8.2 3842/43 95 97 100 3844/45 47 48 V V PWM Section Max. Duty Cycle Min. Duty Cycle Total Standby Current Start−Up Current D(MAX) D(MAX) IST 384X 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 50 % 0 2 30 0.17 0.3 13 17 38 mA V 友台半导体有限公司 UMW R UMW UC3842/43/44/45 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 3842 3844 3843 3845 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 UMW R UMW UC3842/43/44/45 VREF VREF 8 RT 8 RT RT /CT 4 RSLOPE RT /CT 3842 RSLOPE IS 4 3842 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 UC3842/43/44/45 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 UC3842/43/44/45 Typical Performance Characteristics RT (K )Ω % 50 50 C 30 5nF C 20 20 10 10 5nF C C C 5 2nF C 1nF 500pF C 10nF 200pF 5 C C 10nF 100pF 3 2 1 10 500 20 VCC = 2 VCC = 15 O 25 T C 30 50 100 200 300 KHz) f 15 V O T 1 10 500 20 30 50 100 200 = 25 300 KHz) f Figure 2. Output Dead-Time vs. Oscillator Frequenc .y Figure 1. Timing Resistor vs. Oscillator Frequency. Dm ax (%) (dB) 90 80 80 60 70 40 VCC = 15 V VO = 2V to 4V 100K R = L 60 T 50 C 20 15 V V = CC 25 O 3.3nF = 25 0 40 -20 1 3 2 5 Figure 3. Maximum Output Duty Cycle vs. Timing Resistor 3842/4 .3) 10 R (T 100 1K 10K 100K 1M f (Hz) Figure 4. Error Amp Open-Loop Gain vs. .equency Fr Vth ISC (mA) (V) VCC = 15V 1.0 VCC = 15 V 100 90 0.8 T 25 C O 80 0.6 T 125 C O 0.4 70 0.2 60 50 0 2 4 V 0 ( O 75 100 O T ) Figure 6. Reference Short Circuit Current vs. Temperature. Figure 5. Current Sense Input Threshold vs. Error Amp Output Voltage. www.umw-ic.com 25 50 6 友台半导体有限公司 ., UMW R UMW UC3842/43/44/45 Vsat ICC (V) (m A) Sourse Saturation (Load to Ground) -1 V -2 15 V 80 sµ Rate 20 Pulsed Load 120Hz 3 15 2 10 Sink Sa tura tion 1 I = Se nse 0V 10K R TA = 25 C 3.3nF C 5 (Lo a d to 0 0V 0 0 200 Figure Current 400 600 I 0 (O m 10 20 .7 Output Saturation Voltage vs. Load T 25 . Figure .8 Voltag .e 30 V ( CC Supply Current vs. Supply VCC 7 Vref 8 R /C T 5V REG T OUTPUT PWM RT R C T /T 6 4 LARGE R / SMALL C T OUTPUT CLOCK OSCILLATOR R /C T T ID OUTPUT SMALL RT / LARGE 5 GND Figure 9. Oscillator and Output Waveforms www.umw-ic.com 7 友台半导体有限公司