UC2842B/3B/4B/5B UC3842B/3B/4B/5B HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER . . .. . . .. . TRIMMED OSCILLATOR FOR PRECISE FREQUENCY CONTROL OSCILLATOR FREQUENCY GUARANTEED AT 250kHz CURRENT MODE OPERATION TO 500kHz AUTOMATIC FEED FORWARD COMPENSATION LATCHING PWM FOR CYCLE-BY-CYCLE CURRENT LIMITING INTERNALLY TRIMMED REFERENCE WITH UNDERVOLTAGE LOCKOUT HIGH CURRENT TOTEM POLE OUTPUT UNDERVOLTAGE LOCKOUT WITH HYSTERESIS LOW START-UP AND OPERATING CURRENT Minidip SO8 comparatorwhich alsoprovidescurrent limit control, and a totem pole output stage designed to source or sink high peakcurrent. The outputstage, suitable for driving N-Channel MOSFETs, is low in the offstate. Differences between members of this family are the under-voltagelockout thresholds and maximum duty cycle ranges. The UC3842B and UC3844B have UVLO thresholds of 16V (on) and 10V (off), ideally suitedoff-lineapplicationsThecorrespondingthresholdsforthe UC3843BandUC3845Bare8.5 V and7.9 V. The UC3842B and UC3843B can operate to duty cycles approaching 100%. A range of the zero to < 50 % is obtained by the UC3844B and UC3845B by the addition of an internal toggle flip flopwhich blanks the output off every otherclock cycle. DESCRIPTION TheUC384xB family ofcontrolICs providesthe necessary features to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal external parts count. Internally implemented circuits include a trimmed oscillator for precise DUTY CYCLE CONTROL under voltage lockoutfeaturingstart-up current less than0.5mA,a precision reference trimmed for accuracy at the error amp input, logicto insure latched operation,a PWM BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B) Vi 7 UVLO 34V GROUND 5 S/R 8 5V REF INTERNAL BIAS 2.50V VREF GOOD LOGIC RT/CT VFB COMP CURRENT SENSE 4 2 1 3 6 - ERROR AMP. OUTPUT T OSC + VREF 5V 50mA 2R R S 1V R CURRENT SENSE COMPARATOR PWM LATCH UC3842B D95IN331 August 1996 1/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B ABSOLUTE MAXIMUM RATINGS Symbol Parameter Vi Supply Voltage (low impedance source) Vi Supply Voltage (Ii < 30mA) IO Output Current EO Output Energy (capacitive load) Valu e Un it 30 V Self Limiting 1 5 Analog Inputs (pins 2, 3) - 0.3 to 5.5 J V Error Amplifier Output Sink Current Ptot Power Dissipation at Tamb 25 C (Minidip) Ptot Power Dissipation at Tamb 25 C (SO8) Tstg Storage Temperature Range TL Lead Temperature (soldering 10s) A 10 mA 1.25 W 800 mW - 65 to 150 C 300 C * All voltages are with respect to pin 5, all currents are positive into the specified terminal. PIN CONNECTION (top view) Minidip/SO8 COMP 1 8 VREF VFB 2 7 Vi ISENSE 3 6 OUTPUT RT/CT 4 5 GROUND D95IN332 PIN FUNCTIONS No Function 1 COMP Description 2 VFB This is the inverting input of the Error Amplifier. It is normally connected to the switching power supply output through a resistor divider. 3 ISENSE A voltage proportional to inductor current is connected to this input. The PWM uses this information to terminate the output switch conduction. 4 RT/CT The oscillator frequency and maximum Output duty cycle are programmed by connecting resistor RT to Vref and cpacitor CT to ground. Operation to 500kHz is possible. 5 GROUND This pin is the combined control circuitry and power ground. 6 OUTPUT This output directly drives the gate of a power MOSFET. Peak currents up to 1A are sourced and sunk by this pin. 7 VCC This pin is the positive supply of the control IC. 8 Vref This is the reference output. It provides charging current for capacitor CT through resistor RT. This pin is the Error Amplifier output and is made available for loop compensation. ORDERING NUMBERS SO8 UC2842BD1; UC2843BD1; UC2844BD1; UC2845BD1; 2/15 UC3842BD1 UC3843BD1 UC3844BD1 UC3845BD1 Minidip UC2842BN; UC2843BN; UC2844BN; UC2845BN; UC3842BN UC3843BN UC3844BN UC3845BN UC2842B/3B/4B/5B - UC3842B/3B/4B/5B THERMAL DATA Symbo l Rth j-amb Description Thermal Resistance Junction-ambient. Minid ip SO 8 Unit 100 150 C/W max. ELECTRICAL CHARACTERISTICS ( [note 1] Unless otherwise stated, these specifications apply for -25 < Tamb < 85C for UC284XB; 0 < Tamb < 70C for UC384XB; Vi = 15V (note 5); RT = 10K; CT = 3.3nF) Symbo l Parameter T est Cond it ion s UC284XB UC384XB Min. Typ. Max. Min. Typ. Max. Uni t REFERENCE SECTION VREF Output Voltage Tj = 25C Io = 1mA V REF Line Regulation 12V Vi 25V V REF Load Regulation 1 Io 20mA VREF/T Temperature Stability eN ISC 4.95 5.00 5.05 4.90 5.00 5.10 (Note 2) 2 20 3 25 0.2 Total Output Variation Line, Load, Temperature Output Noise Voltage 10Hz f 10KHz Tj = 25C (note 2) 50 Long Term Stability Tamb = (note 2) 5 125C, 1000Hrs Output Short Circuit OSCILLATOR SECTION fOSC Frequency 4.9 -30 49 Tj = 25C 48 TA = Tlow to Thigh TJ = 25C (RT = 6.2k, CT = 1nF) 225 2 20 mV 3 25 mV 0.2 5.1 4.82 mV/C 5.18 5 V V 50 25 V 25 mV -100 -180 -30 -100 -180 mA 52 - 250 55 56 275 49 48 225 52 - 250 55 56 275 KHz KHz KHz fOSC/V Frequency Change with Volt. VCC = 12V to 25V - 0.2 1 - 0.2 1 % fOSC/T Frequency Change with Temp. TA = Tlow to Thigh - 1 - - 0.5 - % VOSC Oscillator Voltage Swing (peak to peak) Idischg Discharge Current (VOSC =2V) TJ = 25C TA = Tlow to Thigh ERROR AMP SECTION V2 Input Voltage Ib VPIN1 = 2.5V - 1.6 - - 1.6 - V 7.8 7.5 8.3 - 8.8 8.8 7.8 7.6 8.3 - 8.8 8.8 mA mA 2.45 2.50 2.55 2.42 2.50 2.58 Input Bias Current VFB = 5V AVOL 2V Vo 4V 65 Unity Gain Bandwidth TJ = 25C Power Supply Rejec. Ratio Io Output Sink Current Io Output Source Current VPIN2 = 2.3V VPIN1 = 5V VOUT High VPIN2 = 2.3V; R L = 15K to Ground VPIN2 = 2.7V; R L = 15K to Pin 8 BW PSRR VOUT Low CURRENT SENSE SECTION GV Gain V3 SVR Ib -0.1 65 0.7 1 12V Vi 25V 60 70 VPIN2 = 2.7V VPIN1 = 1.1V 2 -2 V A 90 dB 0.7 1 MHz 60 70 dB 12 2 12 mA -0.5 -1 -0.5 -1 mA 5 6.2 5 6.2 V 0.8 2.85 Maximum Input Signal VPIN1 = 5V (note 3) 0.9 Supply Voltage Rejection 12 Vi 25V (note 3) Delay to Output -0.1 90 (note 3 & 4) Input Bias Current -1 1.1 3 3.15 2.85 1 1.1 70 0.9 0.8 1.1 V 3 3.15 V/V 1 1.1 70 V dB -2 -10 -2 -10 A 150 300 150 300 ns 3/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B ELECTRICAL CHARACTERISTICS (continued) Symbo l Parameter T est Cond itions UC284XB UC384XB Min . Typ . Max. Min. T yp. Max. Un it OUTPUT SECTION VOL VOH VOLS Output Low Level Output High Level ISINK = 20mA 0.1 0.4 0.1 0.4 V ISINK = 200mA 1.6 2.2 1.6 2.2 V ISOURCE = 20mA 13 13.5 ISOURCE = 200mA 12 13.5 13 13.5 12 13.5 V V UVLO Saturation VCC = 6V; ISINK = 1mA 0.1 1.1 0.1 1.1 V tr Rise Time Tj = 25C CL = 1nF (2) 50 150 50 150 ns tf Fall Time Tj = 25C CL = 1nF (2) 50 150 50 150 ns UNDER-VOLTAGE LOCKOUT SECTION Start Threshold Min Operating Voltage After Turn-on X842B/4B 15 16 17 14.5 16 17.5 V X843B/5B 7.8 8.4 9.0 7.8 8.4 9.0 V X842B/4B 9 10 11 8.5 10 11.5 V X843B/5B 7.0 7.6 8.2 7.0 7.6 8.2 V PWM SECTION Maximum Duty Cycle X842B/3B 94 96 100 94 96 100 % X844B/5B 47 48 50 47 48 50 % 0 % Minimum Duty Cycle 0 TOTAL STANDBY CURRENT Ist Ii V iz Start-up Current Vi = 6.5V for UCX843B/45B 0.3 0.5 0.3 0.5 mA Vi = 14V for UCX842B/44B 0.3 0.5 0.3 0.5 mA 12 17 12 17 mA Operating Supply Current VPIN2 = VPIN3 = 0V Zener Voltage Ii = 25mA 30 36 30 36 V Notes : 1. Max package power dissipation limits must be respected; low duty cycle pulse techniques are used during test maintain Tj as close to Tamb as possible. 2. These parameters, although guaranteed, are not 100% tested in production. 3. Parameter measured at trip point of latch with V PIN2 = 0. 4. Gain defined as : VPIN1 A= ; 0 VPIN3 0.8 V VPIN3 5. Adjust Vi above the start threshold before setting at 15 V. 4/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 1: Open Loop Test Circuit. VREF 4.7K RT 2N2222 100K ERROR AMP. ADJUST COMP ISENSE ADJUST 5K 7 Vi 2 3 RT/CT OUTPUT 6 4 1W 1K 0.1F UC2842B ISENSE Vi 0.1F 8 1 VFB 1K 4.7K A VREF OUTPUT GROUND 5 CT GROUND D95IN343 High peak currents associatedwith 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 5 K potentiometerareusedto samplethe oscillator waveform and apply an adjustable ramp to pin 3. Figure 2: Timing Resistor vs. Oscillator Frequency Figure 3: Output Dead-Time vs. Oscillator Frequency RT D95IN334 D95IN333 % (K) C 50 T= 20 0p F 50 C T= 10 CT=2nF 0p C F T= 30 50 F C CT=5nF CT=5nF 0p 20 20 T= 1n CT=1nF F CT=10nF 10 CT=500pF 10 5 CT=200pF 5 CT =2nF CT=100pF CT=10nF 3 2 2 Vi=15V Vi =15V TA=25C 1 T A=25C 0.8 10K 1 20K 30K 50K 100K 200K 300K 500K f OSC(KHz) 10K 20K 30K 50K 100K 200K 300K 500K fOSC(KHz) 5/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 4: Oscillator Discharge Current vs. Temperature. I dischg (mA) Figure 5: Maximum Output Duty Cycle vs. Timing Resistor. D95IN336 D95IN335 Dmax (%) Vi=15V VOSC=2V 90 8.5 Idischg=7.5mA 80 Idischg=8.8mA 70 8.0 60 Vi=15V CT=3.3nF TA=25C 7.5 50 40 7.0 -55 -25 0 25 50 75 100 TA(C) Figure 6: Error Amp Open-Loop Gain and Phase vs. Frequency. D95IN337 (dB) Vi=15V VO=2V to 4V RL=100K TA=25C 80 Gain 60 0.8 1 2 3 RT(K) 5 Figure 7: Current Sense Input Threshold vs. Error Amp Output Voltage. 30 Vth (V) D95IN338 Vi=15V 1.0 TA=25C 60 0.8 90 0.6 20 120 0.4 0 150 0.2 180 f(Hz) 0.0 TA=125C 40 Phase -20 10 100 1K 10K 100K 1M Figure 8: Reference Voltage Change vs. Source Current. D95IN339 60 Vi=15V 50 TA=-40C 0 2 4 6 Figure 9: Reference Short Circuit Current vs. Temperature. D95IN340 ISC (mA) Vi=15V RL0.1 100 TA=-40C 40 VO(V) 90 TA=125C 30 TA=25C 80 20 70 10 0 0 6/15 60 50 20 40 60 80 100 Iref(mA) -55 -25 0 25 50 75 100 TA(C) UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 10: Output Saturation Voltagevs. Load Current. Ii (mA) D95IN341 Vi -1 -2 Source Saturation (Load to Ground) TA=25C TA=-40C D95IN342 20 Vi=15V 80s Pulsed Load 120Hz Rate 15 UCX843/45 3 10 TA=-40C 2 TA=25C 5 1 Sink Saturation (Load to Vi) 0 0 200 400 R T=10K C T=3.3nF V FB=0V I Sense=0V T A=25C UCX842/44 Vsat (V) Figure 11: Supply Current vs. Supply Voltage. GND 0 600 IO(mA) Figure 12: Output Waveform. 0 10 20 30 Vi(V) Figure 13: Output Cross Conduction Vi =30V CL = 15pF TA = 25C Vi =15V CL = 1.0nF TA = 25C 90% VO 20V/DIV ICC 10% 100mA/DIV 50ns/DIV 100ns/DIV Figure 14: Oscillator and Output Waveforms. Vi 7 8 CT 5V REG OUTPUT PWM 6 LARGE RT/SMALL CT OUTPUT RT CLOCK 4 OSCILLATOR CT ID OUTPUT CT 5 SMALL RT/LARGE CT GND D95IN344 7/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 15 : Error Amp Configuration. 2.5V 1mA + VFB 2 COMP 1 Zi - Zf D95IN345 Figure 16 : Under Voltage Lockout. 7 Vi ON/OFF COMMAND TO REST OF IC ICC UC3842B UC3843B UC3844B UC3845B VON 16V 8.4V VOFF 10V 7.6V <17mA <0.5mA VOFF VON D95IN346 VCC During UVLO, the Output is low Figure 17 : Current Sense Circuit . ERROR AMPL. IS COMP R RS C 1 3 CURRENT SENSE 5 GND D95IN347 Peak current (is) is determined by the formula 1.0 V IS max RS A small RC filter may be required to suppress switch transients. 8/15 2R R 1V CURRENT SENSE COMPARATOR UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 18 : Slope Compensation Techniques. VREG VREG 8 RT RT RT/CT IS RSLOPE 4 CT R1 8 RT/CT IS UC3842B R1 3 5 RS UC3842B CT RSLOPE ISENSE 4 ISENSE 3 5 RS GND GND D95IN348 Figure 19 : Isolated MOSFET Drive and Current Transformer Sensing. VCC Vin 7 + 5.0Vref ISOLATION BOUNDARY - VGS Waveforms Q1 6 + + 0 - S R Q 50% DC Ipk = - + 0 - V(pin 1) -1.4 3RS 25% DC NS ( ) NP + COMP/LATCH R 3 C RS NS NP D95IN349 9/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 20 : Latched Shutdown. 4 OSC 8 R BIAS R + 1mA 2R + - 2 EA R 1 5 2N 3905 2N 3903 D95IN350 SCR must be selected for a holding current of less than 0.5mA at TA(min). The simple two transistor circuit can be used in place of the SCR as shown. All resistors are 10K. Figure 21: Error Amplifier Compensation From VO + 2.5V 1mA Ri - 2 Rd 2R + Cf EA R Rf 1 5 Error Amp compensation circuit for stabilizing any current-mode topology except for boost and flyback converters operating with continuous inductor current. From VO + 2.5V 1mA RP Ri 2 CP Rd 2R + Cf Rf - EA R 1 5 D95IN351 Error Amp compensation circuit for stabilizing current-mode boost and flyback topologies operating with continuous inductor current. 10/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 22: External Clock Synchronization. VREF 8 R BIAS R RT 4 EXTERNAL SYNC INPUT OSC + CT 0.01F 2R + 47 - 2 EA R 1 5 D95IN352 The diode clamp is required if the Sync amplitude is large enough to cause the bottom side of CT to go more than 300mV below ground Figure 23: External Duty Cycle Clamp and Multi Unit Synchronization. 8 VREF RA R RB 5K 8 6 + 5 + C S - 4 + Q 5K R 3 R - 2 BIAS 4 7 2 5K NE555 1 OSC 2R + - EA R 1 5 f= 1.44 (RA + 2RB)C Dmax = RB TO ADDITIONAL UCX84XAs D95IN353 RA + 2RB 11/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 24: Soft-Start Circuit 8 5Vref R + BIAS - R 4 OSC + 1mA 2 Q + - 1M S 2R + EA R R - 1V 1 C 5 D95IN354 Figure 25: Soft-Start and Error Amplifier Output Duty Cycle Clamp. VCC Vin 7 + 8 5Vref R + BIAS 7 - R 4 1mA 2 R2 R 5 Q + EA Q1 S VClamp 2R + - 6 OSC + R 1V 1 Comp/Latch 5 C R1 RS BC109 VCLAMP = * 12/15 R1 R1 + R2 where 0 <VCLAMP <1V Ipk(max) = VCLAMP RS D95IN355 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B SO8 PACKAGE MECHANICAL DATA mm DIM. MIN. TYP. A a1 inch MAX. MIN. TYP. 1.75 0.1 0.069 0.25 a2 MAX. 0.004 0.010 1.6 0.063 a3 0.65 0.85 0.026 0.033 b 0.35 0.48 0.014 0.019 b1 0.19 0.25 0.007 0.010 0.5 0.010 0.020 C 0.25 c1 45 (typ.) D 4.8 5.0 0.189 0.197 E 5.8 6.2 0.228 0.244 e 1.27 0.050 e3 3.81 0.150 F 3.8 4.0 0.15 0.157 L 0.4 1.27 0.016 0.050 M S 0.6 0.024 8 (max.) 13/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B MINIDIP PACKAGE MECHANICAL DATA mm DIM. MIN. A TYP. MAX. MIN. 3.32 TYP. MAX. 0.131 a1 0.51 0.020 B 1.15 1.65 0.045 0.065 b 0.356 0.55 0.014 0.022 b1 0.204 0.304 0.008 0.012 D E 10.92 7.95 9.75 0.430 0.313 0.384 e 2.54 0.100 e3 7.62 0.300 e4 7.62 0.300 F 6.6 0.260 I 5.08 0.200 L 14/15 inch 3.18 3.81 0.125 0.150 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of SGS-THOMSON Microelectronics. 1996 SGS-THOMSON Microelectronics All Rights Reserved SGS-THOMSON Microelectronics GROUP OF COMPANIES Australia - Brazil - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco - The Netherlands - Singapore Spain - Sweden - Switzerland - Taiwan - Thaliand - United Kingdom - U.S.A. 15/15