E-UC3845BN

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 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 offstate. Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. The UC3842B and UC3844B have UVLO thresholds of 16V (on) and 10V (off), ideally suited off-line applications The corresponding thresholds for the UC3843B and UC3845B are 8.5 V and 7.9 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 flop which blanks the output off every other clock cycle. DESCRIPTION The UC384xB 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 a trimmed oscillator for precise DUTY CYCLE CONTROL under voltage lockout featuring start-up current less than 0.5mA, a precision reference trimmed for accuracy at the error amp input, logic to insure latched operation, a PWM BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B) Vi 7 UVLO 34V GROUND S/R 5 8 5V REF INTERNAL BIAS 2.50V VREF GOOD LOGIC RT/CT VFB COMP CURRENT SENSE 4 2 1 3 6 OSC + - ERROR AMP. VREF 5V 50mA OUTPUT T 2R R S 1V R CURRENT SENSE COMPARATOR PWM LATCH UC3842B D95IN331 March 1999 1/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B ABSOLUTE MAXIMUM RATINGS Symbol Parameter Vi Supply Voltage (low impedance source) Vi IO Supply Voltage (Ii < 30mA) EO Output Energy (capacitive load) Value Unit 30 V Self Limiting ±1 5 Output Current Analog Inputs (pins 2, 3) A – 0.3 to 5.5 µJ V 10 1.25 mA W Error Amplifier Output Sink Current Ptot Power Dissipation at Tamb ≤ 25 °C (Minidip) Ptot Power Dissipation at Tamb ≤ 25 °C (SO8) Storage Temperature Range 800 mW – 65 to 150 Junction Operating Temperature – 40 to 150 °C °C 300 °C Tstg TJ TL Lead Temperature (soldering 10s) * 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 C T 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 Symbol Rth j-amb Description Thermal Resistance Junction-ambient. Minidip SO8 Unit 100 150 °C/W max. ELECTRICAL CHARACTERISTICS ( [note 1] Unless otherwise stated, these specifications apply for -25 < Tamb < 85°C for UC284XB; 0 < Tamb < 70°C for UC384XB; Vi = 15V (note 5); RT = 10K; CT = 3.3nF) Symbol Parameter REFERENCE SECTION VREF Output Voltage Test Conditions Line Regulation 12V ≤ Vi ≤ 25V ∆VREF Load Regulation 1 ≤ Io ≤ 20mA ∆VREF/∆T Temperature Stability eN ISC (Note 2) 10Hz ≤ f ≤ 10KHz Tj = 25°C (note 2) 50 Long Term Stability Tamb = (note 2) 5 125°C, -30 VOSC Oscillator Voltage Swing (peak to peak) Idischg Discharge Current (VOSC =2V) TJ = 25°C TA = Tlow to Thigh V3 Ib µV 50 25 5 V 25 mV 55 56 275 KHz KHz KHz – 0.2 1 – 0.2 1 % – 1 – – 0.5 – % – 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 TJ = 25°C Output Sink Current -0.1 -1 -0.1 90 65 0.7 1 12V ≤ Vi ≤ 25V 60 70 VPIN2 = 2.7V VPIN1 = 1.1V 2 -2 V µA 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 (note 3 & 4) 2.85 Maximum Input Signal VPIN1 = 5V (note 3) 0.9 Supply Voltage Rejection 12 ≤ Vi ≤ 25V (note 3) Delay to Output mV/°C 5.18 52 – 250 Power Supply Rejec. Ratio Input Bias Current 4.82 49 48 225 Unity Gain Bandwidth CURRENT SENSE SECTION GV Gain mV 55 56 275 65 VPIN2 = 2.3V VPIN1 = 5V 25 52 – 250 2V ≤ Vo ≤ 4V VPIN2 = 2.3V; RL = 15KΩ to Ground VPIN2 = 2.7V; RL = 15KΩ to Pin 8 3 mA AVOL Output Source Current mV -100 -180 VFB = 5V VOUT High 20 -30 Input Bias Current VOUT Low SVR VPIN1 = 2.5V 2 0.2 5.1 V -100 -180 49 Tj = 25°C 48 TA = Tlow to Thigh TJ = 25°C (RT = 6.2k, CT = 1nF) 225 TA = Tlow to Thigh ERROR AMP SECTION V2 Input Voltage 4.9 1000Hrs Output Short Circuit Frequency Change with Temp. Io 25 Output Noise Voltage ∆fOSC/∆T Io 3 Line, Load, Temperature Frequency Change with Volt. VCC = 12V to 25V BW 20 0.2 ∆fOSC/∆V PSRR 2 Total Output Variation OSCILLATOR SECTION fOSC Frequency Ib 4.95 5.00 5.05 4.90 5.00 5.10 Tj = 25°C Io = 1mA ∆VREF UC284XB UC384XB Unit Min. Typ. Max. Min. Typ. Max. 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 µA 150 300 150 300 ns 3/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B ELECTRICAL CHARACTERISTICS (continued) Symbol Parameter Test Conditions UC284XB UC384XB Unit Min. Typ. Max. Min. Typ. Max. 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 13 13.5 V ISOURCE = 200mA 12 13.5 12 13.5 V UVLO Saturation VCC = 6V; ISINK = 1mA 0.1 1.1 0.1 1.1 V tr Rise Time Tj = 25°C CL = 1nF (2) 50 150 50 150 ns tf Fall Time Tj = 25°C 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 X842B/3B 94 96 100 94 96 100 % X844B/5B 47 48 50 47 48 50 % 0 % PWM SECTION Maximum Duty Cycle Minimum Duty Cycle 0 TOTAL STANDBY CURRENT Ist Ii Viz 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 VPIN2 = 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 RT 4.7KΩ 2N2222 100KΩ COMP 1KΩ ISENSE ADJUST 4.7KΩ 5KΩ 7 Vi 2 3 RT/CT OUTPUT 6 4 1W 1KΩ 0.1µF UC2842B ISENSE Vi 0.1µF 8 1 VFB ERROR AMP. ADJUST A VREF OUTPUT GROUND 5 CT GROUND D95IN343 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 5 KΩ potentiometer are used to sample the 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 (KΩ) D95IN333 D95IN334 % C 50 T= 20 0p F T= 10 0p C T= 50 20 CT=5nF 50 C F C CT=2nF 30 0p F CT=5nF 20 T= 1n F CT=1nF 10 5 CT=10nF CT=100pF 3 2 2 Vi=15V TA=25˚C 1 0.8 10K CT=200pF 5 CT=2nF CT=10nF CT=500pF 10 Vi=15V TA=25˚C 20K 30K 50K 100K 200K 300K 500K fOSC(KHz) 1 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. Idischg (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=25˚C 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=25˚C 80 Gain 60 0.8 1 2 3 5 RT(KΩ) Figure 7: Current Sense Input Threshold vs. Error Amp Output Voltage. φ 30 Vth (V) D95IN338 Vi=15V 1.0 TA=25˚C 60 0.8 90 0.6 20 120 0.4 0 150 0.2 180 f(Hz) 0.0 TA=125˚C 40 Phase -20 10 100 1K 10K 100K 1M Figure 8: Reference Voltage Change vs. Source Current. D95IN339 60 Vi=15V 50 TA=-40˚C 0 2 4 6 Figure 9: Reference Short Circuit Current vs. Temperature. D95IN340 ISC (mA) Vi=15V RL≤0.1Ω 100 TA=-40˚C 40 VO(V) 90 TA=125˚C 30 TA=25˚C 80 20 70 10 60 0 50 0 6/15 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=25˚C TA=-40˚C D95IN342 20 Vi=15V 80µs Pulsed Load 120Hz Rate 15 UCX843/45 3 10 TA=-40˚C 2 TA=25˚C 5 1 Sink Saturation (Load to Vi) 0 0 200 400 RT=10K CT=3.3nF VFB=0V ISense=0V TA=25˚C 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 = 25°C Vi =15V CL = 1.0nF TA = 25°C 90% VO 20V/DIV ICC 10% 100mA/DIV 50ns/DIV 100ns/DIV Figure 14: Oscillator and Output Waveforms. Vi CT 7 8 5V REG OUTPUT PWM 6 RT LARGE RT/SMALL CT OUTPUT 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