Fairchild FAN6751 High-Performance Green-Mode PWM Controller Data Handbook

www.fairchildsemi.com

AN-6073 FAN6751 — Highly Integrated Green-Mode PWM Controller

Introduction Internal Open-loop Protection GATE Output Maximum Voltage Clamp: 18V

This application note describes a detailed design strategy for

a high-efficiency, compact flyback converter. Design VDD Under-Voltage Lockout (UVLO)

considerations and mathematical equations are presented as

VDD Over-Voltage Protection (OVP)

well as guidelines for a printed circuit board layout. The

Internal Recovery Circuit (OVP, OLP)

highly integrated FAN6751 series of PWM controllers provides several features to enhance the performance for Internal Sense Short-Circuit Protection LCDM/TV, NB, and adapters.

External Constant Power Limit (Full AC Input Range)

The green-mode function includes off-time modulation and

Internal OTP Sensor with Hysteresis

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

Built-in 5ms Soft-Start Function

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

minimum PWM frequency is set above 18KHz. This green- Built-in VIN Pin Pull HIGH (> 4.7V) Recovery mode function enables the power supply to meet Function for Second-Side Output OVP

international power conservation requirements. With the

Brownout Protection with Hysteresis

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 Applications

control. The proprietary external line compensation ensures

General-purpose, switch-mode power supplies and flyback

constant output power limit over a wide AC input voltage

power converters, including:

range, from 90VAC to 264VAC.

Power Adapters

FAN6751 provides many protection functions, as shown in

Open-frame SMPS

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

internal open-loop protection circuit ensures safety should LCD Monitor/TV

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

SOP-8

Features High-Voltage Startup

GND GATE

Low Operating Current: 4m A

FB VDD

Linearly Decreasing PWM Frequency to 18KHz

Fixed PWM Frequency: 65KHz NC SENSE

Peak-Current-Mode Control

HV VIN

Cycle-by-Cycle Current Limiting

Leading-Edge Blanking (LEB) Figure 1. Pin Configuration (Top View)

Synchronized Slope Compensation

Table 1. Protection Functions of FAN6751 Series

OTP SCP PWM

Part Number OVP (VDD) OLP (FB) Pull-High

Protection (VIN) (Internal) (SENSE) Frequency

FAN6751MRMY Recovery Recovery Recovery Recovery Recovery 65KHz FAN6751HLMY Latch Latch Latch Recovery Recovery 100KHz

© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.0 • 9/26/08