Features

• Synchronous Rectifier Control for High Efficiency
• Programmable Volt-Second Clamp
• Output Power Levels from 25W to 500W
• Low Current Start-Up
  (LT1952: 460µA; V_IN On/Off = 14.25V/8.75V)
  (LT1952-1: 400µA; V_IN On/Off = 7.75V/6.5V)
• True PWM Soft-Start
• Low Stress Short Circuit Protection
• Precision 107mV Current Limit Threshold
• Adjustable Delay for Synchronous Timing
• Accurate Shutdown Threshold with Programmable Hysteresis
• Programmable Slope Compensation
• Programmable Leading Edge Blanking
• Programmable Frequency (100kHz to 500kHz)
• Synchronizable to an External Clock up to 1.5 · f_OSC
• Internal 1.23V Reference
• 2.5V External Reference
• Current Mode Control
• Small 16-Pin SSOP Package

Typical Application

Description

The LT1952/LT1952-1 are current mode PWM controllers optimized to control the forward converter topology, using one primary MOSFET. The LT1952/LT1952-1 provide synchronous rectifier control, resulting in extremely high efficiency. A programmable Volt-Second clamp provides a safeguard for transformer reset that prevents saturation. This allows a single MOSFET on the primary side to reliably run at greater than 50% duty cycle for high MOSFET, transformer and rectifier utilization. The devices include soft-start for controlled exit from shutdown and undervoltage lockout. A precision 107mV current limit threshold, independent of duty cycle, combines with softstart to provide hiccup short circuit protection. The LT1952 is optimized for micropower bootstrap startup from high input voltages. The LT1952-1 allows startup from lower input voltages. Programmable slope compensation and leading edge blanking allow optimization of loop bandwidth with a wide range of inductors and MOSFETs. Each device can be programmed over a 100kHz to 500kHz frequency range and the part can be synchronized to an external clock. The error amplifier is a true op amp, allowing a wide range of compensation networks. The LT1952/LT1952-1 are available in a small 16-pin SSOP package.