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SG6741A

Highly Integrated Green-Mode PWM Controller

Fairchild Semiconductor 

October 2008

SG6741A

Highly Integrated Green-Mode PWM Controller

Features

ƒ High-Voltage Startup

ƒ Low Operating Current: 4mA

ƒ Linearly Decreasing PWM Frequency to 18kHz

ƒ Frequency Hopping to Reduce EMI Emissions

ƒ Peak-Current-Mode Control

ƒ Cycle-by-Cycle Current Limiting

ƒ Leading-Edge Blanking (LEB)

ƒ Synchronized Slope Compensation

ƒ GATE Output Maximum Voltage Clamp: 18V

ƒ VDD Over-Voltage Protection (Auto Restart)

ƒ VDD Under-Voltage Lockout (UVLO)

ƒ Internal Open-Loop Protection

ƒ Constant Power Limit (Full AC Input Range)

Applications

General-purpose switch-mode power supplies and

flyback power converters, including:

ƒ Power Adapters

ƒ Open-Frame SMPS

Description

The highly integrated SG6741A series of PWM

controllers provides several features to enhance the

performance of flyback converters.

To minimize standby power consumption, a proprietary

green-mode function provides off-time modulation to

linearly decrease the switching frequency at light-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 eliminated. To further

reduce power consumption, SG6741A is manufactured

using the BiCMOS process, which allows an operating

current of only 4mA.

SG6741A integrates a frequency-hopping function

internally to reduce EMI emission of a power supply

with minimum line filters. A built-in synchronized slope

compensation achieves stable peak-current-mode

control. The proprietary internal line compensation

ensures constant output power limit over a wide AC

input voltages, from 90VAC to 264 VAC.

SG6741A provides many protection functions. In

addition to cycle-by-cycle current limiting, the internal

open-loop protection circuit ensures safety when an

open-loop or output short-circuit failure occurs. PWM

output is disabled until VDD drops below the UVLO lower

limit, when the controller starts up again. As long as VDD

exceeds ~26V, the internal OVP circuit is triggered.

SG6741A is available in an 8-pin SOP package.

Ordering Information

Part Number

Operating

Temperature Range

Package

SG6741ASZ

SG6741ASY

-40 to +105°C

-40 to +105°C

8-Lead Small Outline Package (SOP)

8-Lead Small Outline Package (SOP)

Eco

Status

Green

Green

Packing Method

Tape & Reel

Tape & Reel

For Fairchild’s definition of “green” Eco Status, please visit: http://www.fairchildsemi.com/company/green/rohs_green.html.

© 2008 Fairchild Semiconductor Corporation

SG6741A • Rev. 1.0.1

www.fairchildsemi.com

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