Philips Semiconductors Linear Products Product specification Current-mode PWM controller UC3842 DESCRIPTION PIN CONFIGURATIONS The UC3842 is available in an 8-Pin mini-DIP the necessary features to implement off-line, fixed-frequency current-mode control schemes with a minimal external parts count. This technique results in improved line regulation, enhanced load response characteristics, and a simpler, easier to design control loop. Topological advantages include inherent pulse-by-pulse current limiting. N Package Protection circuitry includes built-in undervoltage lock-out and current limiting. Other features include fully-latched operation, a 1% trimmed bandgap reference, and start-up current less than 1mA. COMP 1 8 VREF VFB 2 7 VCC ISENSE 3 6 OUTPUT RT/CT 4 5 GROUND TOP VIEW These devices feature a totem-pole output designed to source and sink high peak current from a capacitive load, such as the gate of a power MOSFET. Consistent with N-channel power devices, the output is low in the OFF-state. D Package COMP 1 14 VREF NC 2 13 NC 3 12 V CC FEATURES * Low start-up current (1mA) * Automatic feed-forward compensation * Pulse-by-pulse current limiting * Enhanced load response characteristics * Undervoltage lock-out with hysteresis * Double pulse suppression * High current totem-pole output * Internally-trimmed bandgap reference * 400kHz operation, guaranteed min VFB NC 4 11 V C ISENSE 5 10 OUTPUT NC 6 9 GROUND RT/CT 7 8 POWER GROUND TOP VIEW APPLICATIONS * Off-line switched mode power supplies * DC-to-DC converters UC3842 BLOCK DIAGRAM 7(11) (12)7 VCC UVLO 34V (9)5 S/R GND 6V V 8(14) REF 5.0V 50mA 5V REF 16V 2.5V INTERNAL BIAS (7)4 OSC RT/CT 6(10) OUTPUT ERROR AMP VFB (3)2 + - S 2R R PWM LATCH R COMP CURRENT SENSE (1)1 1V CURRENT SENSE COMPARATOR (5)3 5(8) NOTE: Pin numbers in parentheses refer to the D package. August 31, 1994 1100 853-0614 13721 Philips Semiconductors Linear Products Product specification Current-mode PWM controller UC3842 ORDERING INFORMATION DESCRIPTION TEMPERATURE RANGE ORDER CODE DWG # 8-Pin Plastic Dual In-Line Package (DIP) 0 to +70C UC3842N 0404B 14-Pin Plastic Small Outline (SO) Package 0 to +70C UC3842D 0405B ABSOLUTE MAXIMUM RATINGS1 SYMBOL PARAMETER RATING UNIT VCC Supply voltage (ICC<30mA) Self-Limiting VCC Supply voltage (low impedance source) 30 IOUT Output current 2, 3 1 A Output energy (capacitive load) 5 J Analog inputs (Pin 2, Pin 3) PD -0.3 to 6.3 V Error amp output sink current 10 mA Power dissipation at TA70C 1 W -65 to +150 C 300 C (derate 12.5mW/C for TA >70C)2 TSTG Storage temperature range TSOLD Lead temperature (soldering, 10sec max) NOTES: 1. All voltages are with respect to Pin 5; all currents are positive into the specified terminal. 2. See section in application note on "Power Dissipation Calculation". 3. This parameter is guaranteed, but not 100% tested in production. August 31, 1994 V 1101 Philips Semiconductors Linear Products Product specification Current-mode PWM controller UC3842 DC AND AC ELECTRICAL CHARACTERISTICS 0TJ70C for UC3842; VCC=15V; RT=10kW; CT=3.3nF, unless otherwise specified. SYMBOL PARAMETER TEST CONDITIONS UC3842 UNIT Min Typ Max 4.90 5.00 5.10 V Reference section VOUT Output voltage TJ=25C, IO=1mA Line regulation 12VIN25V 6 20 mV Load regulation 1IO20mA 6 25 mV Temp. stability1 Total output variation1 VNOISE Output noise voltage1 0.2 Line, load, temp. 4.82 0.4 mV/C 5.18 V V 10Hzf10kHz, TJ=25C 50 Long-term stability1 TJ=125C, 1000 Hrs. 5 25 mV Output short-circuit TJ=25 -30 -100 -130 mA Output short-circuit -55<TJ0C -30 -100 -180 mA Initial accuracy TJ=25C 47 52 57 kHz Voltage stability 12VCC25V 0.2 1 % Oscillator section Temp. stability1 Amplitude TMINTJTMAX 5 % VPIN 4 peak-to-peak 1.7 V Error amp section Input voltage IBIAS V Pin 1=2.5V 2.42 2VO4V 65 90 dB 1 MHz Input bias current AVOL Unity gain bandwidth1 Unity gain bandwidth PSRR Power supply rejection ratio ISINK Output sink current ISOURCE Output source current TJ=25C 0.7 TMIN<TJ<TMAX 0.5 2.50 2.58 V -0.3 -2 A MHz 12VCC25V 60 70 dB VPIN 2=2.7V, VPIN 1=1.1V 2 6 mA mA VPIN 2=2.3V, VPIN 1=5V -0.5 -0.8 VOUT High VPIN 2=2.3V, RL=15k to ground 5 6 VOUT Low VPIN 2=2.7V, RL=15k to Pin 8 V 0.7 1.1 V 2.85 3 3.15 V/V 0.9 1 1.1 Current sense section Gain 2, 3 Maximum input signal2 VPIN 1=5V 12VCC25V V PSRR Power supply rejection ratio2 IBIAS Input bias current -2 -10 A Delay to output1 150 300 ns August 31, 1994 1102 70 dB Philips Semiconductors Linear Products Product specification Current-mode PWM controller UC3842 DC AND AC ELECTRICAL CHARACTERISTICS 0TJ70C for UC3842; VCC=154; RT=10k; CT=3.3nF, unless otherwise specified SYMBOL PARAMETER UC3842 TEST CONDITIONS Min Typ Max ISINK=20mA 0.1 0.4 ISINK=200mA 1.5 2.2 UNIT Output section VOL Output Low-Level VOH Output High-Level tR Rise time CL=1nF 50 150 ns tF Fall time CL=1nF 50 150 ns ISOURCE=20mA 13 13.5 ISOURCE=200mA 12 13.5 V V Undervoltage lockout section Start threshold 14.5 16 17.5 V Min. operating voltage after turn on 8.5 10 11.5 V 93 97 100 PWM section Maximum duty cycle Minimum duty cycle 0 % Total standby current Start-up current ICC Operating supply current VCC zener voltage 0.5 1 mA VPIN 2=VPIN 3=0V 11 17 mA ICC=25mA 34 V Maximum operating frequency section Maximum operating frequency for all functions operating cycle-by-cycle 400 kHz NOTES: 1. These parameters, although guaranteed, are not 100% tested in production. 2. Parameter measured at trip point of latch with VPIN 2=0. V PIN 1 3. Gain defined as: ; 0 V PIN 3 0.8V A V PIN 3 UNDERVOLTAGE LOCKOUT ERROR AMP CONFIGURATION 7 2.5V ON/OFF COMMAND TO REST OF IC VCC 0.5mA + ZI 2 VFB - 1 VON UC3842 16V VOFF 10V COMP NOTE: Error AMP can source or sink up to 0.5mA. ICC <15mA <1mA VOFF VON VCC NOTE: During Undervoltage Lock-Out, the output driver is biased to a high impedance state. Pin 6 should be shunted to ground with a bleeder resistor to prevent activating the power switch with output leakage current. August 31, 1994 1103 Philips Semiconductors Linear Products Product specification Current-mode PWM controller UC3842 CURRENT SENSE CIRCUIT ERROR AMP 2R IS CURRENT SENSE COMPARATOR R 1 1V COMP R 3 CURRENT SENSE RS 5 GND NOTE: Peak current (IS) is determined by the formula: I S MAX 1.0V Rs A small RC filter may be required to suppress switch transients. TYPICAL PERFORMANCE CHARACTERISTICS Output Saturation Characteristics Error Amplifier Open-Loop Frequency Response 4 45 3 2 1 0 80 0 Av 60 40 -90 20 -135 0 -180 -20 10 0 0.01 0.03 0.05 0.1 0.3 0.5 1.0 OUTPUT CURRENT, SOURCE OR SINK (A) August 31, 1994 1104 -45 100 1k 10k 100k 1M FREQUENCY (Hz) -225 10M PHASE (DEG) VOLTAGE GAIN (dB) SATURATION VOLTAGE (V) 100 Philips Semiconductors Linear Products Product specification Current-mode PWM controller UC3842 OPEN-LOOP LABORATORY TEST FIXTURE VREF A RT VCC 2N2222 4.7k 100k 1 UC3842 COMP ERROR AMP ADJUST 2 5k ISENSE ADJUST 0.1F 7 VCC VFB 0.1F 1k 1W 6 3 4.7k 8 VREF OUTPUT OUTPUT 5 ISENSE 4 GND RT/CT GND CT NOTE: 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. SHUTDOWN TECHNIQUES 4.7k 8 1 COMP 3 4.7k SHUTDOWN ISENSE 500 SHUTDOWN TO CURRENT SENSE RESISTOR NOTE: Shutdown of the UC3842 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 Pins 1 and/or 3 is removed. In the examples shown, an externally-latched shutdown may be accomplished by adding an SCR which will be reset by cycling VCC below the lower UVLO threshold (10V). At this point all internal bias is removed, allowing the SCR to reset. August 31, 1994 1105 Philips Semiconductors Linear Products Product specification Current-mode PWM controller UC3842 OFF-LINE FLYBACK REGULATOR T1 4.7 1W USD735 + 4.7k 4W 220F 250V 673-3 0.01F 400V 56k 1W 4700F 10V DC (5V 2-5A) OUT 1N3613 AC INPUT - 1N3613 16V 10F 20V VCC 7 20k 820pF 1N3613 0.01F UC3842 2.5k 2 VFB 150k 6 27 OUT 1 UFN432 20k COMP 3.6k NOTES: T1: Coilcraft E-4140-B Primary - 97 turns single AWG24 Secondary - 4 turns 4 parallel AWG22 control - 9 turns -3 parallel AWG28 3 100pF CUR SEN 8 VREF 10k 1k 470pF 0.85 4 RT/CT 0.01F 0.0047F GND ISOLATION BOUNDARY 5 SPECIFICATIONS Input line voltage: NOTE: This circuit uses a low-cost feedback scheme in which the DC voltage developed from the primary-side control winding is sensed by the UC3842 error amplifier. Load regulation is therefore dependent on the coupling between secondary and control windings, and on transformer leakage inductance. For applications requiring better load regulation, a UC1901 Isolated Feedback Generator can be used to directly sense the output voltage. 90VAC to 130VAC Input frequency: 50 or 60Hz Switching frequency: 40kHz10% Output power: 25W maximum Output voltage: 5V5% Output current: 2 to 5A Line regulation: 0.01%/V Load regulation: 8%/A* Efficiency @ 25 W, VIN=90VAC: 70% VIN=130VAC: 65% Output short-circuit current: August 31, 1994 2.5A average 1106 Philips Semiconductors Linear Products Product specification Current-mode PWM controller UC3842 SYNCHRONIZATION AND MAXIMUM DUTY CYCLE CLAMP 5V VCC 4 RA 8 RESET 7 VCC 7 DISCH RB NE555 OUT 3 RT/CT 4 UC3842 2 TRIG 6 THRESH 5 GND GND C 1 NOTES: TO OTHER UC3842s 1.44 f + (R A ) 2R B) C D MAX August 31, 1994 + RB RA ) 2R B 1107