www.fairchildsemi.com UC3846 SMPS Controller Features Description * Automatic Feed Forward Compensation * Programmable Pulse by Pulse Current Limiting * Automatic Symmetry Correction in Push-Pull Configuration * Enhanced Load Response Characteristics * Parallel Operation Capability for Modulator Power Systems * Differential Current Sense Amplifier with Common Mode Range * Double Pulse Suppression * 200mA Totem-Pole Outputs * 2% Band gap Reference * Under-Voltage Lockout * Soft-Start Capability * Shutdown Terminal * 500KHz Operation The UC3846 control IC provides all of the necessary features to implement fixed frequency, current mode control schemes while maintaining a minimum external parts count. The superior performance of this technique can be measured 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 capability, automatic symmetry correction for push-pull converters, and the ability to parallel "power module,, while maintaining equal current sharing. Protection circuitry includes built-in-under-voltage lockout and programmable current limit in addition to soft-start capability. A shutdown function is also available which can initiate either a complete shutdown with automatic restart or latch the supply off. Other features include fully latched operation, double pulse suppression, deadtime adjust capability, and 2% trimmed bandgap reference. The UC3846 features low outputs in the OFF state. 16-DIP 1 Internal Block Diagram 10 Rev. 5.0 (c)2000 Fairchild Semiconductor International UC3846 Absolute Maximum Ratings Parameter Supply Voltage Collector Supply Voltage Output Current, Sink of Source (Peak) Symbol Value Unit VCC 40 V VC 40 V IO 500 mA IREF 30 mA ISINK(S.S) 50 mA Sync Output Current ISYNC 5 mA Error Amplifier Output Current IO(E.A) 5 mA Reference Output Current Soft Start Sink Current ICHG(OSC) 5 mA PD 1000 mW Operating Temperature TOPR 0 ~ +70 C Storage Temperature TSTG -65 ~ +150 C Lead Temperature (Soldering, 10sec) TLEAD +300 C Oscillator Changing Current Power Dissipation (TA = 25C) Electrical Characteristics (VCC=15V, TA=0C to +70C, unless otherwise specified) Parameter Symbol Conditions Min. Typ. Max. Unit 5.00 5.10 5.20 V 5 20 mV REFERENCE SECTION Reference Output Voltage TJ = 25C, IREF = 1mA Line Regulation VREF VCC = 8 to 40V - Load Regulation VREF IREF1 to 10mA - 3 15 mV - - 0.4 1.0 mV/C Line,Load,Temp 4.95 - 5.25 V -10 -45 - mA Temperature Stability(Note 6) Output Voltage Range (Note 6) STT VREF Short Circuit Output Current ISC VREF = 0V Output Noise Voltage(Note 6) VNO f = 10Hz to 10KHz, TJ = 25C - 100 - uV TJ = 125C, 1KHz 2 5 8 mV Long-Term Stability(Note 6) 2 VREF ST UC3846 Electrical Characteristics (VCC= 15V,TA=0C to +70C, unless otherwise specified) Parameter Symbol Conditions Min. Typ. Max. Unit 39 43 47 KHz OSCILLATOR SECTION (Note 2) Initial Accuracy ACCUR TJ = 25C Frequency Change with Voltage f/VCC VCC = 8 to 40V - 1 2 % Frequency Change with Temperature (Note 6) f/T - - 1 - % Sync Output High Level VOH(SYNC) - 3.9 4.35 - V Sync Output Low Level VOL(SYNC) - - 2.3 2.5 V Sync Input High Level VIH(SYNC) V8 = 0V 3.9 - - V Sync Input Low Level VIL(SYNC) Sync Input Current V8 = 0V - - 2.5 V II(SYNC) Sync Voltage = 3.9V, V8 = 0V - 1.3 1.5 mA VIO - - 0.5 5 mV IBIAS - - -0.6 -1 uA ERROR AMPLIFIER SECTION Input Offset Voltage Input Bias Current Input Offset Current IIO - - 40 250 uA Common-Mode Range VCM VCC = 8 to 40V 0 - VCC2 V Open Loop Voltage Gain GVO VO = 1.2 to 3V, VCM = 2V 80 105 - dB Unity Gain Bandwidth(Note 6) BW TJ = 25C 0.7 1.0 - MHz dB Common Mode Rejection Ratio CMRR VCM = 0 to 38V, VCC = 40V 75 100 - Power Supply Rejection Ratio PSRR VCC = 8 to 40V 80 105 - dB Output Sink Current ISINK VIO = -15mV to 5V, V7 = 2.5V 2 6 - mA ISOURCE RL = 15K -0.4 -0.5 - mA High Output Voltage VOH RL = 15K 4.3 4.6 - V Low Output Voltage VOL - 0.7 1 V V3 = 0V, Pin 1 open 2.5 2.75 3.0 V VI(DIFF,MAX) RL = 15K, Pin 1 open 1.1 1.2 - V VIO V1 = 0.5V, Pin 1 open - 5 25 mV Output Source Current - CURRENT SENSE AMPLIFIER SECTION Amplifier Gain (Note 1, 3) Maximum Differential Input Signal (V4 - V3) (Note 1) Input Offset Voltage (Note 1) GV Common Mode Rejection Ratio CMRR VCM = 1 to 12V 60 83 - dB Power Supply Rejection Ratio PSRR VCC = 8 to 40V 60 84 - dB Input Bias Current (Note 1) IBIAS V1 = 0.5V, Pin 7 open - -2.5 -10 uA Input Offset Current (Note 1) IIO V1 = 0.5V, Pin 7 open - 0.08 1 uA Delay to Outputs (Note 6) tD TJ = 25C - 200 500 ns 3 UC3846 Electrical Characteristics (VCC=15V, TA=0C to + 70C, unless otherwise specified) Parameter Symbol Conditions Min. Typ. Max. Unit VIO(C.L) V3 = 0V V4 = 0V, Pin 7 open 0.45 0.5 0.55 V IBIAS V5 = VREF, V6 = 0V - - 10 - 30 uA VTH - 250 350 400 mV VI - 0 - VCC V I(LATCH,MIN) - 3.0 1.5 - mA - - 1.5 0.8 mA VTH(ST) - 7 7.7 8.4 V VHYS - 0.45 0.75 1.05 V - CURRENT LIMIT ADJUST SECTION Current Limit Offset Voltage (Note 1) Input Bias Current SHUTDOWN TERMINAL SECTION Threshold Voltage Input Voltage Range Minimum Latching Current (Note 4) Maximum Non-Latching Current (Note 5) I(NONLATCH,MAX) UNDER-VOLTAGE LOCKOUT SECTION Start Threshold Threshold Hysteresis OUTPUT SECTION Collector-Emitter Voltage VCEO 40 - - V Collector Leakage Current ILEAK VC = 40V - - 200 uA Low Output Voltage 1 VOL 1 ISINK = 20mA - 0.1 0.4 V Low Output Voltage 2 VOL 2 ISINK = 100mA - 0.4 2.1 V High Output Voltage 1 VOH 1 ISOURCE = 20mA 13 13.5 - V High Output Voltage 2 VOH 2 ISOURCE = 100mA 12 13.5 - V Rise Time (Note 6) tR CL = 1nF, TJ = 25C - 50 300 us Fall Time (Note 6) tF CL = 1nF, TJ = 25C - 50 300 us ICC - - 17 21 mA TOTAL STANDBY CURRENT Supply Current Notes : 1. Parameter measured at trip point at latch with V5 = VREF, V6 = 0V 2. RT = 10K, CT = 4.7nF 3. Amplifier gain definde as: V7 G = ----------- ;V 4 = 0to1.0V V4 4. Current into Pin 1 guaranteed to latch circuit in shutdown state. 5. Current into Pin 1 guaranteed not to latch circuit in shutdown state. 6. These parameters, although guaranteed over the recommended operating conditions, are not 100% tested in production. 4 UC3846 Td OUTPUT DEADTIME(Td) Figure 1. UC3846 Oscillator Circuit 12 Output deadtime is determined by the external capacitor, CT, according to the formula: Td ( us ) = 145C T ( F ) ---------------------------------- 3.6 12 - --------------------- For large values of RT: Td (us) = l45CT (uF) Oscillator frequency is approximately R T ( K ) 2.2 by the formula: fT ( KHz ) = ----------------------------------------R T ( K )C T ( F ) Figure 2. Error Amplifier Output Configuration 5 UC3846 Figure 3. Parallel Operation Figure 4. Pulse By Pulse Current Limiting Figure 5. Current Sense Amp Connections A small PC filter may be required in some applications to reduce switch transients Differential input allows remote, noise free sensing. 6 UC3846 Mechanical Dimensions Package 16-DIP #9 7.62 0.300 2.54 0.100 1.50 0.10 0.059 0.004 #8 0.46 0.10 0.018 0.004 #16 19.80 MAX 0.780 #1 19.40 0.20 0.764 0.008 ( 0.81 ) 0.032 6.40 0.20 0.252 0.008 3.25 0.20 0.128 0.008 5.08 MAX 0.200 0.38 0.014 MIN 3.30 0.30 0.130 0.012 +0.10 0~15 0.25 -0.05 +0.004 0.010 -0.002 7 UC3846 Ordering Information 8 Product Number Package Operating Temperature UC3846N 16 DIP 0 ~ + 70C UC3846 9 UC3846 LIFE SUPPORT POLICY FAIRCHILD'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR INTERNATIONAL. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user. 2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com 7/12/00 0.0m 001 Stock#DSxxxxxxxx 2000 Fairchild Semiconductor International