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FAN6793MY

Highly Integrated, Dual-PWM Combination Controller

Fairchild Semiconductor 

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

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