FAN6791 Datasheet, PDF (1/19 Pages) Fairchild Semiconductor – Highly Integrated, Dual-PWM Combination Controller

April 2009
FAN6791 / FAN6793
Highly Integrated, Dual-PWM Combination Controller
Features
ƒ High-Voltage Startup
ƒ Low Operating Current
ƒ Interleaved Stand-by PWM / Forward PWM Switching
ƒ Green Mode Stand-by PWM / Forward PWM
ƒ Linearly Decreasing Stand-by PWM Frequency to
20kHz
ƒ Remote On / Off
ƒ AC Brownout Protection
ƒ Forward PWM with Soft-Start
ƒ Frequency Hopping to Reduce EMI Emissions
ƒ Cycle-by-Cycle Current Limiting for Stand-by PWM /
Forward PWM
ƒ Leading-Edge Blanking for Stand-by PWM / Forward
PWM
ƒ Synchronized Slope Compensation for Stand-by
PWM / Forward PWM
ƒ GATE Output Maximum Voltage Clamp
ƒ VDD Over-Voltage Protection (OVP)
ƒ VDD Under-Voltage Lockout (UVLO)
ƒ Internal Open-Loop Protection for Stand-by PWM /
Forward PWM
ƒ Constant Power Limit for Stand-by PWM / Forward
PWM
Description
The highly integrated FAN6791/3 dual PWM
combination controller provides several features to
enhance the performance of 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 20KHz. 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, FAN6791/3 is
manufactured using the CMOS process, which allows
an operating current of only 6mA.
FAN6791/3 integrates a frequency-jittering function
internally to reduce EMI emissions of a power supply
with minimum line filters. The built-in synchronized slope
compensation achieves stable peak-current-mode
control. The proprietary internal line compensation
ensures constant output power limit.
FAN6791/3 provides many protection functions,
including brownout protection, cycle-by-cycle current
limiting, and an internal open-loop protection circuit to
ensure safety should an open-loop or output short-
circuit failure occur. PWM output is disabled until VDD
drops below the UVLO lower limit when the controller
restarts. As long as VDD exceeds ~24.5V, the internal
OVP circuit is triggered.
Applications
General-purpose switch-mode power supplies and
flyback power converters, including:
ƒ PC-ATX Power Supplies
© 2008 Fairchild Semiconductor Corporation
FAN6791 / FAN6793 • Rev. 1.0.2
www.fairchildsemi.com