LT1950 Single Switch PWM Controller with Auxiliary Boost Converter FEATURES DESCRIPTIO The LT 1950 is a wide input range, forward, boost, flyback Wide Input Range: 3V to 25V and SEPIC controller that drives an N-channel power Programmable Volt-Second Clamp MOSFET with few external components required. Output Power Levels from 25W to 500W Auxiliary Boost Converter Provides 10V Gate Drive A resistor programmable duty cycle clamp can be used to from V as Low as 3V IN generate a volt-second clamp for forward converter appli- Programmable Operating Frequency (100kHz to cations. An internal boost switcher is available for creating 500kHz) with One External Resistor a separate supply for the output gate driver, allowing 10V Programmable Slope Compensation gate drive from input voltages as low as 3V. The LT1950s Programmable Leading Edge Blanking operating frequency can be set with an external resistor 2% Internal 1.23V Reference over a 100kHz to 500kHz range and a SYNC pin allows the Accurate Shutdown Pin Threshold with part to be synchronized to an external clock. Additional Programmable Hysteresis programmability exists for leading edge blanking and 60ns Current Sense Delay slope compensation. 2.5V Auxiliary Reference Output A fast current sense comparator achieves 60ns current Synchronizable to an External Clock up to 1.5 f OSC sense delay and the error amplifier is a true voltage mode Current Mode Control error amplifier, allowing a wide range of compensation Small 16-Pin SSOP Package U networks. An accurate shutdown pin with programmable APPLICATIO S hysteresis is available for undervoltage lockout and shut- down. The LT1950 is available in a small 16-Pin SSOP Telecom Power Supplies package. Automotive Power Supplies Portable Electronic Equipment , LTC and LT are registered trademarks of Linear Technology Corporation. Isolated and Nonisolated DC/DC Converters TYPICAL APPLICATIO 36V to 72V DC to 26V/5A (Single Switch) Forward Converter Efficiency vs Load Current 95 10V V BIAS IN 47H MBRB20200 V V = 36V OUT IN 26V SLOPE V IN 90 5A V = 48V IN 2.5V 47F 470k V V REF IN2 V = 72V IN 0.1F BOOST V PA0581 SEC 85 R SHDN OSC 1F 18k 249k LT1950 80 Si7450 BLANK GATE SYNC I 75 SENSE GND PGND 0.015 FB COMP 70 4.99k 4.7k 0.5 1.5 2.5 3.5 4.5 5.5 100k 0.022F LOAD CURRENT (A) 1950 TA01a 1950 TA01b 1950fa 1 EFFICIENCY (%) U ULT1950 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) ORDER PART TOP VIEW BOOST ....................................................... 0.3V to 35V NUMBER COMP 1 16 V V , V , SHDN ......................................... 0.3V to 25V SEC IN IN2 2 FB 15 V IN FB, SYNC, V ........................................... 0.3V to 6V SEC LT1950EGN 3 R 14 BOOST OSC COMP, BLANK .......................................... 0.3V to 3.5V 4 LT1950IGN SYNC 13 PGND SLOPE ...................................................... 0.3V to 2.5V 5 SLOPE 12 GATE 6 11 V V REF IN2 I ......................................................... 0.3V to 1V SENSE 7 10 SHDN I SENSE R .................................................................... 50A OSC GN PART MARKING 8 9 GND BLANK V .................................................................... 10mA REF GN PACKAGE 1950E 16-LEAD NARROW PLASTIC SSOP Operating Junction Temperature Range T = 125C, = 110C/W, 1950I JMAX JA LT1950EGN/LT1950IGN (Notes 2, 5) ... 40C to 125C (PIN 8) = 30C/W JC Storage Temperature Range ..................65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25C. COMP = open, FB = 1.4V, R = 249k, SYNC = 0V, SLOPE = open, V A OSC REF = 0.1F, SHDN = V , BLANK = 0V, I = 0V, V = 15V, GATE = 1nF, BOOST = open, V = 15V, V = 0V, unless otherwise IN SENSE IN2 IN SEC specified. PARAMETER CONDITIONS MIN TYP MAX UNITS PWM Controller Operating Input Voltage I = 0A 3.0 25 V VREF Minimum Start-Up Voltage I = 0A 2.6 3.0 V VREF V Quiescent Current I = 0A, FB = 1V, I = 0.2V 2.3 3.0 mA IN VREF SENSE V Shutdown Current SHDN = 0V 5 20 A IN Shutdown Threshold 3V < V < 25V 1.261 1.32 1.379 V IN Shutdown Pin Current SHDN = 70mV Above Threshold 7 10 13 A Shutdown Pin Current Hysteresis SHDN = 100mV Below Threshold 4 7 10 A V Quiescent Current I(V ) = 0A, FB = 1V, I = 0.2V 1.7 2.5 mA IN2 REF SENSE V Shutdown Current SHDN = 0V, V = 2.7V (Boost Diode from V = 3V) 500 700 A IN2 IN2 IN V (External Output) REF Output Voltage I = 0A 2.425 2.500 2.575 V VREF Line Regulation I = 0A, 3V < V < 25V 1 5 mV VREF IN Load Regulation 0A < I < 2.5mA 1 5 mV VREF Oscillator Frequency: f R = 249k, FB = 1V 170 200 230 kHz OSC OSC Minimum Programmable f R = 499k 85 100 115 kHz OSC OSC Maximum Programmable f R = 90.9k 440 500 560 kHz OSC OSC SYNC Input Resistance 20 k SYNC Switching Threshold 1.5 2.2 V SYNC Frequency/f (R = 249k, f =200kHz), FB = 1V (Note 7) 1.25 1.5 OSC OSC OSC f Line Reg 3V < V < 25V 0.05 0.15 %/V OSC IN 9.5V < V < 25V 0.05 0.25 %/V IN2 V 1V ROSC 1950fa 2 U WWW