LM5021

AC-DC Current Mode PWM Controller

General Description

The LM5021 off-line pulse width modulation (PWM) control-

ler contains all of the features needed to implement highly

efficient off-line single-ended flyback and forward power con-

verters using current-mode control. The LM5021 features

include an ultra-low (25 µA) start-up current, which mini-

mizes power losses in the high voltage start-up network. A

skip cycle mode reduces power consumption with light loads

CECP, etc.). Additional features include under-voltage lock-

out, cycle-by-cycle current limit, hiccup mode overload pro-

tection, slope compensation, soft-start and oscillator syn-

chronization capability. This high performance 8-pin IC has

total propagation delays less than 100nS and a 1MHz ca-

pable oscillator that is programmed with a single resistor.

Features

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Ultra Low Start-up Current (25 µA maximum)

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Current Mode Control

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Skip Cycle Mode for Low Standby Power

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Single Resistor Programmable Oscillator

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Synchronizable Oscillator

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Adjustable Soft-start

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Integrated 0.7A Peak Gate Driver

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Direct Opto-Coupler Interface

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Maximum Duty Cycle Limiting (80% for LM5021-1 or

50% for LM5021-2)

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Slope Compensation for (LM5021-1 Only)

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Under Voltage Lockout (UVLO) with Hysteresis

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Cycle-by-Cycle Over-Current Protection

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Hiccup Mode for Continuous Overload Protection

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Leading Edge Blanking of Current Sense Signal

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Packages: MSOP-8 or MDIP-8

Simplified Application Diagram

20144201

May 2005

© 2005 National Semiconductor Corporation

DS201442

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