LT1950 Single Switch PWM Controller with Auxiliary Boost Converter UFEATURESDESCRIPTIO ■ Wide Input Range: 3V to 25V The LT®1950 is a wide input range, forward, boost, flyback ■ Programmable Volt-Second Clamp and SEPIC controller that drives an N-channel power ■ Output Power Levels from 25W to 500W MOSFET with few external components required. ■ Auxiliary Boost Converter Provides 10V Gate Drive A resistor programmable duty cycle clamp can be used to from VIN as Low as 3V 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 LT1950’s ■ 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 ■ Synchronizable to an External Clock up to 1.5 • f A fast current sense comparator achieves 60ns current OSC ■ Current Mode Control sense delay and the error amplifier is a true voltage mode ■ Small 16-Pin SSOP Package error amplifier, allowing a wide range of compensation U networks. An accurate shutdown pin with programmable APPLICATIO S hysteresis is available for undervoltage lockout and shut- ■ Telecom Power Supplies down. The LT1950 is available in a small 16-Pin SSOP ■ Automotive Power Supplies package. ■ Portable Electronic Equipment ■ Isolated and Nonisolated DC/DC Converters , LTC and LT are registered trademarks of Linear Technology Corporation. UTYPICAL APPLICATIO36V to 72V DC to 26V/5A (Single Switch) Forward ConverterEfficiency vs Load Current 10V 95 BIAS VIN MBRB20200 47µH VOUT VIN = 36V 26V SLOPE VIN 5A 90 V 2.5V IN = 48V 470k 47µF VREF VIN2 VIN = 72V 0.1µF BOOST VSEC PA0581 85 ROSC SHDN 1µF 249k 18k LT1950 80 EFFICIENCY (%) BLANK GATE Si7450 SYNC ISENSE 75 GND PGND 0.015Ω FB COMP 70 4.99k 4.7k 0.5 1.5 2.5 3.5 4.5 5.5 0.022µF 100k LOAD CURRENT (A) 1950 TA01a 1950 TA01b 1950fa 1
