1 Features

• Ultra-low Startup Current (25 µA Maximum)
• Current Mode Control
• Skip Cycle Mode for Low Standby Power
• Single Resistor Programmable Oscillator
• Synchronizable Oscillator
• Adjustable Soft-Start
• Integrated 0.7-A Peak Gate Driver
• Direct Opto-Coupler Interface
• Maximum Duty Cycle Limiting (80% for LM5021-1 or 50% for LM5021-2)
• Slope Compensation (LM5021-1 Only)
• Undervoltage Lockout (UVLO) with Hysteresis
• Cycle-by-Cycle Overcurrent Protection
• Hiccup Mode for Continuous Overload Protection
• Leading Edge Blanking of Current Sense Signal
• Packages: VSSOP-8 or PDIP-8

2 Applications

• DCM/CCM Flyback Converters
• Industrial Power Conversion
• SMPS for Smart Meters and Audio Amplifiers
• Building Automation and White Goods SMPS
• Isolated Telecom Power Supplies

3 Description

The LM5021 off-line pulse width modulation (PWM) controller contains all of the features needed to implement highly efficient off-line single-ended flyback and forward power converters using current-mode control. The LM5021 features include an ultra-low (25 µA) start-up current, which minimizes power losses in the high voltage start-up network. A skip cycle mode reduces power consumption with light loads for energy conserving applications (ENERGY STAR®, CECP, and so forth). Additional features include under-voltage lockout, cycle-by-cycle current limit, hiccup mode overload protection, slope compensation, soft-start and oscillator synchronization capability. This high performance 8-pin IC has total propagation delays less than 100 ns and a 1-MHz capable oscillator that is programmed with a single resistor.

1. For all available packages, see the orderable addendum at the end of the datasheet.

Simplified Application Diagram