LT1952/LT1952-1 Single Switch Synchronous Forward Controller FEATURES DESCRIPTION n Synchronous Rectifier Control for High Efficiency The LT 1952/LT1952-1 are current mode PWM controllers n Programmable Volt-Second Clamp optimized to control the forward converter topology, using n Output Power Levels from 25W to 500W one primary MOSFET. The LT1952/LT1952-1 provide n Low Current Start-Up synchronous rectifier control, resulting in extremely (LT1952: 460A V On/Off = 14.25V/8.75V) high efficiency. A programmable Volt-Second clamp IN (LT1952-1: 400A V On/Off = 7.75V/6.5V) provides a safeguard for transformer reset that prevents IN n True PWM Soft-Start saturation. This allows a single MOSFET on the primary n Low Stress Short-Circuit Protection side to reliably run at greater than 50% duty cycle for high n Precision 107mV Current Limit Threshold MOSFET, transformer and rectifier utilization. The devices n Adjustable Delay for Synchronous Timing include soft-start for controlled exit from shutdown and n Accurate Shutdown Threshold with Programmable undervoltage lockout. A precision 107mV current limit Hysteresis threshold, independent of duty cycle, combines with soft- n Programmable Slope Compensation start to provide hiccup short-circuit protection. The LT1952 n Programmable Leading Edge Blanking is optimized for micropower bootstrap start-up from high n Programmable Frequency (100kHz to 500kHz) input voltages. The LT1952-1 allows start-up from lower n Synchronizable to an External Clock up to 1.5 f input voltages. Programmable slope compensation and OSC n Internal 1.23V Reference leading edge blanking allow optimization of loop bandwidth n 2.5V External Reference with a wide range of inductors and MOSFETs. Each device n Current Mode Control can be programmed over a 100kHz to 500kHz frequency n Small 16-Pin SSOP Package range and the part can be synchronized to an external clock. The error amplifier is a true op amp, allowing a wide APPLICATIONS range of compensation networks. The LT1952/LT1952-1 are available in a small 16-pin SSOP package. n Telecommunications Power Supplies n Industrial and Distributed Power L, LT, LTC and LTM are registered trademarks and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. n Isolated and Non Isolated DC/DC Converters TYPICAL APPLICATION 36V to 72V Input, 12V at 20A Semi-Regulated Bus Converter 12V Bus Converter L1 V vs V T1 V OUT IN IN PA1494.242 V PA0905 OUT SUPPLY FROM BIAS 12V WINDING OF T1 16 20A 10F 47F V V REF IN 16V 14 X5R 52.3k COMP Si7370 PH4840 2 2 2 Si7450 SS MAXDC OUT V IN LT1952/ OC 12 LT1952-1 340k I 0.005 SENSE 100k SD V SEC LTC3900 10 FB FG CG 13k T2 SYNC SOUT SYNC 8 GND R 220pF 560 OSC 36 42 48 54 60 66 72 V (V) PGND BLANK DELAY IN 0.1F 0.1F 1952 TA01b 40k 40k 178k 1952 TA01 19521fe 1 40k 16V V (V) OUTLT1952/LT1952-1 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW V (Note 8) ...............................................0.3V to 25V IN COMP 1 16 SOUT SYNC, SS MAXDC, SD V , I , OC ....0.3V to 6V SEC SENSE FB 2 15 V IN COMP, BLANK, DELAY ...............................0.3V to 3.5V R 3 14 OUT OSC FB ................................................................0.3V to 3V SYNC 4 13 PGND R ..................................................................... 50A OSC SS MAXDC 5 12 DELAY V ....................................................................10mA REF V 6 11 OC REF Operating Junction Temperature Range (Notes 2, 5) SD V 7 10 I SEC SENSE E-, I-Grades .......................................40C to 125C GND 8 9 BLANK MP-Grade .......................................... 55C to 125C GN PACKAGE 16-LEAD PLASTIC SSOP Storage Temperature Range ...................65C to 150C T = 125C, q = 110C/W, q = 40C/W JMAX JA JC Lead Temperature (Soldering, 10 sec) .................. 300C ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1952EGN PBF LT1952EGN TRPBF 1952 16-Lead Plastic SSOP 40C to 125C LT1952IGN PBF LT1952IGN TRPBF 1952I 16-Lead Plastic SSOP 40C to 125C LT1952MPGN PBF LT1952MPGN TRPBF 1952 16-Lead Plastic SSOP 55C to 125C LT1952EGN-1 PBF LT1952EGN-1 TRPBF 19521 16-Lead Plastic SSOP 40C to 125C LT1952IGN-1 PBF LT1952IGN-1 TRPBF 1952I1 16-Lead Plastic SSOP 40C to 125C LT1952MPGN-1 PBF LT1952MPGN-1 TRPBF 19521 16-Lead Plastic SSOP 55C to 125C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1952EGN LT1952EGN TR 1952 16-Lead Plastic SSOP 40C to 125C LT1952IGN LT1952IGN TR 1952I 16-Lead Plastic SSOP 40C to 125C LT1952MPGN LT1952MPGN TR 1952 16-Lead Plastic SSOP 55C to 125C LT1952EGN-1 LT1952EGN-1 TR 19521 16-Lead Plastic SSOP 40C to 125C LT1952IGN-1 LT1952IGN-1 TR 1952I1 16-Lead Plastic SSOP 40C to 125C LT1952MPGN-1 LT1952MPGN-1 TR 19521 16-Lead Plastic SSOP 55C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. 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