Datasheet LT1952, LT1952-1 (Analog Devices)

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: 460µA; VIN On/Off = 14.25V/8.75V)
high efficiency. A programmable Volt-Second clamp
(LT1952-1: 400µA; VIN On/Off = 7.75V/6.5V)
provides a safeguard for transformer reset that prevents 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 • fOSC input voltages. Programmable slope compensation and 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 n are available in a small 16-pin SSOP package. 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
V L1
V
IN T1
OUT vs VIN
40k PA0905 PA1494.242 V SUPPLY FROM BIAS OUT 12V WINDING OF T1 20A 16 16V 10µF 47µF VREF VIN 16V 14 52.3k COMP Si7370 PH4840 X5R ×2 ×2 ×2 SS_MAXDC OUT Si7450 VIN LT1952/ (V) OC 12 LT1952-1 340k I V OUT SENSE 0.005Ω 100k SD_VSEC LTC3900 10 13k FB FG CG T2 SYNC SOUT SYNC GND R 8 OSC 220pF 560Ω 36 42 48 54 60 66 72 PGND BLANK DELAY VIN (V) 0.1µF 0.1µF 1952 TA01b 40k 40k 178k 1952 TA01 19521fe 1 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Timing Diagram Block Diagram Operation Applications Information Typical Applications Revision History Package Description Related Parts