UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 Current Mode PWM Controller FEATURES DESCRIPTION • Optimized For Off-line And DC To DC Converters • Low Start Up Current (<1mA) • Automatic Feed Forward Compensation • Pulse-by-pulse Current Limiting • The UC1842/3/4/5 family of control ICs provides the 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 under-voltage lockout featuring start up current less than 1mA, a precision reference trimmed for accuracy at the error amp input, logic to insure latched operation, a PWM comparator which also provides current limit control, and a totem pole output stage designed to source or sink high peak current. The output stage, suitable for driving N Channel MOSFETs, is low in the off state. Enhanced Load Response Characteristics • Under-voltage Lockout With Hysteresis • Double Pulse Suppression • High Current Totem Pole Output • Internally Trimmed Bandgap Reference • 500khz Operation • Low RO Error Amp Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. The UC1842 and UC1844 have UVLO thresholds of 16V (on) and 10V (off), ideally suited to off-line applications. The corresponding thresholds for the UC1843 and UC1845 are 8.4V and 7.6V. The UC1842 and UC1843 can operate to duty cycles approaching 100%. A range of zero to 50% is obtained by the UC1844 and UC1845 by the addition of an internal toggle flip flop which blanks the output off every other clock cycle. BLOCK DIAGRAM Note 1: A/B A = DIL-8 Pin Number. B = SO-14 Pin Number. Note 2: Toggle flip flop used only in 1844 and 1845. 4/97 UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltage (Low Impedance Source) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30V Supply Voltage (ICC <30mA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Self Limiting Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±1A Output Energy (Capacitive Load) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5µJ Analog Inputs (Pins 2, 3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6.3V Error Amp Output Sink Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10mA Power Dissipation at TA ≤ 25°C (DIL-8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1W Power Dissipation at TA ≤ 25°C (SOIC-14) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 725mW Storage Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -65°C to +150°C Lead Temperature (Soldering, 10 Seconds) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300°C Note 1: All voltages are with respect to Pin 5. All currents are positive into the specified terminal. Consult Packaging Section of Databook for thermal limitations and considerations of packages. CONNECTION DIAGRAMS DIL-8, SOIC-8 (TOP VIEW) N or J Package, D8 Package PLCC-20 (TOP VIEW) Q Package PACKAGE PIN FUNCTION FUNCTION PIN N/C COMP N/C N/C VFB N/C ISENSE N/C N/C RT/CT N/C PWR GND GROUND N/C OUTPUT N/C VC VCC N/C VREF SOIC-14 (TOP VIEW) D Package 2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for -55°C ≤ TA ≤ 125°C for the UC184X; -40°C ≤ TA ≤ 85°C for the UC284X; 0°C ≤ TA ≤ 70°C for the 384X; VCC = 15V (Note 5); RT = 10k; CT =3.3nF, TA=TJ. PARAMETER UC1842/3/4/5 UC2842/3/4/5 TEST CONDITIONS UC3842/3/4/5 UNITS MIN TYP MAX MIN TYP MAX 4.95 5.00 5.05 4.90 5.00 5.10 V 6 20 6 20 mV Reference Section Output Voltage TJ = 25°C, IO = 1mA Line Regulation 12 ≤ VIN ≤ 25V Load Regulation 1 ≤ I0 ≤ 20mA Temp. Stability (Note 2) (Note 7) Total Output Variation Line, Load, Temp. (Note 2) Output Noise Voltage 10Hz ≤ f ≤ 10kHz, TJ = 25°C (Note2) 50 Long Term Stability TA = 125°C, 1000Hrs. (Note 2) 5 25 -100 -180 -30 52 57 47 0.2 1 6 25 6 25 mV 0.2 0.4 0.2 0.4 mV/°C 4.9 Output Short Circuit -30 5.1 4.82 5.18 V µV 50 5 25 mV -100 -180 mA 52 57 kHz 0.2 1 % Oscillator Section Initial Accuracy TJ = 25°C (Note 6) Voltage Stability 12 ≤ VCC ≤ 25V Temp. Stability TMIN ≤ TA ≤ TMAX (Note 2) Amplitude VPIN 4 peak to peak (Note 2) 47 5 5 % 1.7 1.7 V Error Amp Section Input Voltage VPIN 1 = 2.5V 2.45 Input Bias Current 2 ≤ VO ≤ 4V 65 Unity Gain Bandwidth (Note 2) TJ = 25°C PSRR 12 ≤ VCC ≤ 25V AVOL Output Sink Current VPIN 2 = 2.7V, VPIN 1 = 1.1V Output Source Current VPIN 2 = 2.3V, VPIN 1 = 5V VOUT High VPIN 2 = 2.3V, RL = 15k to ground VOUT Low VPIN 2 = 2.7V, RL = 15k to Pin 8 2.50 2.55 -0.3 -1 2.42 90 65 0.7 1 60 70 2.50 2.58 V -0.3 -2 µA 90 dB 0.7 1 MHz 60 70 dB 2 6 2 6 mA -0.5 -0.8 -0.5 -0.8 mA 5 6 5 0.7 1.1 3 3.15 2.85 1 1.1 0.9 6 V 0.7 1.1 V 3 3.15 V/V 1 1.1 Current Sense Section Gain (Notes 3 and 4) 2.85 Maximum Input Signal VPIN 1 = 5V (Note 3) 0.9 PSRR 12 ≤ VCC ≤ 25V (Note 3) (Note 2) 70 -2 -10 -2 -10 µA VPIN 3 = 0 to 2V (Note 2) 150 300 150 300 ns Input Bias Current Delay to Output 70 Note 2: These parameters, although guaranteed, are not 100% tested in production. Note 3: Parameter measured at trip point of latch with VPIN 2 = 0. Note 4: Gain defined as ∆ VPIN 1 A= , 0 ≤ VPIN 3 ≤ 0.8V ∆ VPIN 3 Note 5: Adjust VCC above the start threshold before setting at 15V. Note 6: Output frequency equals oscillator frequency for the UC1842 and UC1843. Output frequency is one half oscillator frequency for the UC1844 and UC1845. Note 7: Temperature stability, sometimes referred to as average temperature coefficient, is described by the equation: VREF (max) − VREF (min) Temp Stability = TJ (max) − TJ (min) VREF (max) and VREF (min) are the maximum and minimum reference voltages measured over the appropriate temperature range. Note that the extremes in voltage do not necessarily occur at the extremes in temperature. 3 V dB UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for −55°C ≤ TA ≤ 125°C for the UC184X; −40°C≤ TA ≤ 85°C for the UC284X; 0°C ≤ TA ≤ 70°C for the 384X; VCC = 15V (Note 5); RT = 10k; CT =3.3nF, TA=TJ. PARAMETER UC1842/3/4/5 UC2842/3/4/5 TEST CONDITION MIN UC3842/3/4/5 TYP MAX ISINK = 20mA 0.1 ISINK = 200mA 1.5 MIN UNITS TYP MAX 0.4 0.1 0.4 V 2.2 1.5 2.2 V Output Section Output Low Level Output High Level ISOURCE = 20mA 13 13.5 13 13.5 V ISOURCE = 200mA 12 13.5 12 13.5 V Rise Time TJ = 25°C, CL = 1nF (Note 2) 50 150 50 150 ns Fall Time TJ = 25°C, CL = 1nF (Note 2) 50 150 50 150 ns Under-voltage Lockout Section Start Threshold Min. Operating Voltage After Turn On X842/4 15 16 17 14.5 16 17.5 V X843/5 7.8 8.4 9.0 7.8 8.4 9.0 V X842/4 9 10 11 8.5 10 11.5 V X843/5 7.0 7.6 8.2 7.0 7.6 8.2 V X842/3 95 97 100 95 97 100 % X844/5 46 48 50 47 48 50 % 0 % 0.5 1 mA 11 17 mA PWM Section Maximum Duty Cycle Minimum Duty Cycle 0 Total Standby Current Start-Up Current Operating Supply Current VPIN 2 = VPIN 3 = 0V 0.5 1 11 17 ICC = 25mA 30 34 VCC Zener Voltage Note 2: These parameters, although guaranteed, are not 100% tested in production. Note 3: Parameter measured at trip point of latch with VPIN 2 = 0. Note 4: Gain defined as: ∆ VPIN 1 A= ; 0 ≤ VPIN 3 ≤ 0.8V. ∆ VPIN 3 Note 5: Adjust VCC above the start threshold before setting at 15V. Note 6: Output frequency equals oscillator frequency for the UC1842 and UC1843. Output frequency is one half oscillator frequency for the UC1844 and UC1845. ERROR AMP CONFIGURATION Error Amp can Source or Sink up to 0.5mA 4 30 34 V UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 UNDER-VOLTAGE LOCKOUT During under-voltage lock-out, the output driver is biased to sink minor amounts of current. Pin 6 should be shunted to ground with a bleeder resistor to prevent activating the power switch with extraneous leakage currents. CURRENT SENSE CIRCUIT Peak Current (IS) is Determined By The Formula 1.0V ISMAX ≈ RS A small RC filter may be required to suppress switch transients. OSCILLATOR SECTION 5 UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 ERROR AMPLIFIER OPEN-LOOP FREQUENCY RESPONSE OUTPUT SATURATION CHARACTERISTICS OPEN-LOOP LABORATORY FIXTURE High peak currents associated with 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 5k potentiometer are used to sample the oscillator waveform and apply an adjustable ramp to pin 3. SHUT DOWN TECHNIQUES Shutdown of the UC1842 can be accomplished by two methods; either raise pin 3 above 1V or pull pin 1 below a voltage two diode drops above ground. Either method causes the output of the PWM comparator to be high (refer to block diagram). The PWM latch is reset dominant so that the output will remain low until the next clock cycle after the shutdown condition at pin 1 and/or 3 is removed. In one example, an externally latched shutdown may be accomplished by adding an SCR which will be reset by cycling VCC below the lower UVLO threshold. At this point the reference turns off, allowing the SCR to reset. 6 UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 OFFLINE FLYBACK REGULATOR 5. Output Voltage: A. +5V, ±5%; 1A to 4A load Ripple voltage: 50mV P-P Max B. +12V, ±3%; 0.1A to 0.3A load Ripple voltage: 100mV P-P Max C. -12V ,±3%; 0.1A to 0.3A load Ripple voltage: 100mV P-P Max Power Supply Specifications 1. Input Voltage 2. Line Isolation 3. Switching Frequency 4. Efficiency @ Full Load 95VAC to 130VA (50 Hz/60Hz) 3750V 40kHz 70% SLOPE COMPENSATION A fraction of the oscillator ramp can be resistively summed with the current sense signal to provide slope compensation for converters requiring duty cycles over 50%. Note that capacitor, C forms a filter with R2 to suppress the leading edge switch spikes. UNITRODE CORPORATION 7 CONTINENTAL BLVD. • MERRIMACK, NH 03054 TEL. (603) 424-2410 • FAX (603) 424-3460 7 IMPORTANT NOTICE Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. 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