SG6741A Datasheet, PDF (1/12 Pages) Fairchild Semiconductor – Highly Integrated Green-Mode PWM Controller

April 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 264VAC.
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
-20 to +85°C
8-Lead Small Outline Package (SOP)
All packages are lead free per JEDEC: J-STD-020B standard.
Packing Method
Tape and Reel
© 2008 Fairchild Semiconductor Corporation
SG6741A • Rev. 1.0.0
www.fairchildsemi.com