FAN6751MRMY Просмотр технического описания (PDF) - Fairchild Semiconductor

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FAN6751MRMY

Highly Integrated Green-Mode PWM Controller

Fairchild Semiconductor 

www.fairchildsemi.com

AN-6073

FAN6751 — Highly Integrated Green-Mode PWM Controller

Introduction

This application note describes a detailed design strategy for

a high-efficiency, compact flyback converter. Design

considerations and mathematical equations are presented as

well as guidelines for a printed circuit board layout. The

highly integrated FAN6751 series of PWM controllers

provides several features to enhance the performance for

LCDM/TV, NB, and adapters.

The green-mode function includes off-time modulation and

burst mode to reduce the PWM frequency at light-load and

in no-load conditions. To avoid acoustic noise problems, the

minimum PWM frequency is set above 18KHz. This green-

mode function enables the power supply to meet

international power conservation requirements. With the

internal high-voltage startup circuitry, the power loss due to

bleeding resistors is also eliminated. Built-in synchronized

slope compensation achieves stable peak-current-mode

control. The proprietary external line compensation ensures

constant output power limit over a wide AC input voltage

range, from 90VAC to 264VAC.

FAN6751 provides many protection functions, as shown in

Table 1. In addition to cycle-by-cycle current limiting, the

internal open-loop protection circuit ensures safety should

an open-loop or output short-circuit failure occur.

Features

ƒ High-Voltage Startup

ƒ Low Operating Current: 4mA

ƒ Linearly Decreasing PWM Frequency to 18KHz

ƒ Fixed PWM Frequency: 65KHz

ƒ Peak-Current-Mode Control

ƒ Cycle-by-Cycle Current Limiting

ƒ Leading-Edge Blanking (LEB)

ƒ Synchronized Slope Compensation

ƒ Internal Open-loop Protection

ƒ GATE Output Maximum Voltage Clamp: 18V

ƒ VDD Under-Voltage Lockout (UVLO)

ƒ VDD Over-Voltage Protection (OVP)

ƒ Internal Recovery Circuit (OVP, OLP)

ƒ Internal Sense Short-Circuit Protection

ƒ External Constant Power Limit (Full AC Input Range)

ƒ Internal OTP Sensor with Hysteresis

ƒ Built-in 5ms Soft-Start Function

ƒ Built-in VIN Pin Pull HIGH (> 4.7V) Recovery

Function for Second-Side Output OVP

ƒ Brownout Protection with Hysteresis

Applications

General-purpose, switch-mode power supplies and flyback

power converters, including:

ƒ Power Adapters

ƒ Open-frame SMPS

ƒ LCD Monitor/TV

SOP-8

GND 1

FB 2

NC 3

HV 4

8 GATE

7 VDD

6 SENSE

5 VIN

Figure 1. Pin Configuration (Top View)

Table 1. Protection Functions of FAN6751 Series

Part Number

FAN6751MRMY

FAN6751HLMY

OVP (VDD)

Recovery

Latch

OLP (FB)

Recovery

Latch

Pull-High

Protection (VIN)

Recovery

Latch

© 2008 Fairchild Semiconductor Corporation

Rev. 1.0.0 • 9/26/08

OTP

(Internal)

Recovery

Recovery

SCP

(SENSE)

Recovery

Recovery

PWM

Frequency

65KHz

100KHz

www.fairchildsemi.com

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