SG6741_08 Datasheet, PDF (1/12 Pages) Fairchild Semiconductor – Highly Integrated Green-Mode PWM Controller

October 2008
SG6741
Highly Integrated Green-Mode PWM Controller
Features
ƒ High-Voltage Startup
ƒ Low Operating Current: 4mA
ƒ Linearly Decreasing PWM Frequency to 22kHz
ƒ Frequency Hopping to Reduce EMI Emission
ƒ Peak-Current-Mode Control
ƒ Cycle-by-Cycle Current Limiting
ƒ Leading-Edge Blanking
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 SG6741 PWM controller provides
several features to enhance the performance of flyback
converters.
The highly integrated SG6741 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 22KHz. 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. To further
reduce power consumption, SG6741 is manufactured
using the BiCMOS process, which allows an operating
current of only 4mA.
SG6741 integrates a frequency-hopping function that
helps reduce EMI emission of a power supply with
minimum line filters. Its built-in synchronized slope
compensation achieves stable peak-current-mode
control. The proprietary internal line compensation
ensures constant output power limit over a wide range
of AC input voltages, from 90VAC to 264VAC.
SG6741 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;
then the controller starts again. As long as VDD exceeds
about 26V, the internal OVP circuit is triggered.
SG6741 is available in an 8-pin SOP package.
Ordering Information
Part Number
SG6741SZ
SG6741SY
Operating
Temperature
Range
Package
-40 to +105°C 8-Lead Small Outline Package (SOP)
-40 to +105°C 8-Lead Small Outline Package (SOP)
Eco Status ^{Packing Method}
Green
Green
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
SG6741 • Rev. 1.3.3
1
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