SG684965TZ Datasheet, PDF (1/16 Pages) Fairchild Semiconductor – Low-Power, Green-Mode PWM Flyback Power Controller without Secondary Feedback

December 2008
SG6849
Low-Power, Green-Mode PWM Flyback Power Controller
without Secondary Feedback
Features
ƒ Linearly Decreasing PWM Frequency
ƒ Green-Mode Under Light-Load and Zero-Load
Conditions
ƒ Constant Voltage (CV) and Constant Current (CC)
ƒ No Secondary Feedback
ƒ Low Startup Current: 5μA
ƒ Low Operating Current: 3.6mA
ƒ Leading-Edge Blanking (LEB)
ƒ Constant Power Limit
ƒ Universal AC Input Range
ƒ Synchronized Slope Compensation
ƒ 150°C OTP Sensor with Hysteresis
ƒ VDD Over-Voltage Clamping
ƒ Cycle-by-Cycle Current Limiting
ƒ Under-Voltage Lockout (UVLO)
ƒ Fixed PWM Frequency: 65kHz
ƒ Gate Output Maximum Voltage Clamped at 16.7V
ƒ Small SSOT-6 Package
Applications
Low-power, flyback power converters, such as:
ƒ Battery chargers for cellular phones, cordless
phones, PDAs, digital cameras, and power tools
ƒ Power adapters for ink jet printers, video game
consoles, and portable audio players
ƒ Open-frame SMPS for TV/DVD standby and other
auxiliary supplies, home appliances, consumer
electronics, and PC 5V standby-power
ƒ Replacements for linear transformers and RCC
SMPS
Description
This highly integrated PWM controller provides several
features to enhance the performance of low-power
flyback converters. To minimize standby power
consumption, the proprietary green-mode function
provides off-time modulation to linearly decrease the
switching frequency under light-load and zero-load
conditions. This green-mode function enables the
power supply to meet international power conservation
requirements.
The supply voltage VDD is also used for feedback
compensation to regulate the output voltage without
requiring a conventional TL431 and a photo-coupler. An
advantage of the SG6849 is a typical startup current of
only 5µA, while the typical operating current can be as
low as 3.6mA. A large startup resistance can be used to
achieve even higher power conversion efficiency.
Built-in synchronized slope compensation maintains the
stability of peak current-mode control. Proprietary
internal compensation ensures constant output power
limiting over a universal range of AC input voltages,
from 90VAC to 264VAC.
The SG6849 provides many protection functions. Pulse-
by-pulse current limiting ensures a constant output
current, even if a short circuit occurs. The internal
protection circuit disables PWM output if VDD exceeds
22.7V. The gate output is clamped at 16.7V to protect
the power MOS from over-voltage damage. The built-in
over-temperature protection (OTP) function shuts down
the controller at 150°C with a 20°C hysteresis.
The SG6849 is designed to provide a low-cost total
solution for flyback converters. It is available in a small
footprint, 6-pin, SSOT-6 package.
Related Resources
ƒ AN-6849 - Low Cost, Green-Mode PWM Controller
for Flyback Converters
© 2008 Fairchild Semiconductor Corporation
SG6849 Rev. 1.6.1
www.fairchildsemi.com