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FAN400A — Low-Power Green-Mode PWM Flyback Power Controller without Secondary Feedback
October 2008
FAN400A —
Low-Power Green-Mode PWM Flyback Power
Controller without Secondary Feedback
Features
Linearly Decreasing PWM Frequency
Green Mode Under Light-Load and Zero-Load
Conditions
Constant Voltage (CV) and Constant Current (CC)
No Secondary Feedback
Low Startup Current: 8μA
Low Operating Current: 3.6mA
Leading-Edge Blanking
Constant Power Limit
Universal AC Input Range
Synchronized Slope Compensation
140°C OTP Sensor with Hysteresis
V
DD
Over-Voltage Clamping
Cycle-by-Cycle Current Limiting
Under-Voltage Lockout (UVLO)
Fixed PWM Frequency with Hopping
Gate Output Maximum Voltage Clamped at 17V
Small SSOT-6 Package
Description
This highly integrated PWM controller provides several
features to enhance the performance of low-power
flyback converters. To minimize standby power
consumption, a proprietary green-mode function
provides off-time modulation to linearly decrease the
switching frequency under light-load and zero-load
conditions. This green mode enables the power supply
to meet international power conservation requirements.
The supply voltage V
DD
is also used for feedback
compensation, to regulate the output voltage without
requiring a conventional TL431 and a photo-coupler.
Another advantage of the FAN400A is that the typical
startup current is only 8μA, 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.
FAN400A integrates a frequency hopping function
internally to reduce EMI emissions with minimum line
filters. Built-in synchronized slope compensation
maintains the stability of peak current-mode control.
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