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FAN4800AU

PFC/ PWM Controller Combination

Fairchild Semiconductor 

October 2011

FAN4800AU/CU

PFC/ PWM Controller Combination

Features

 Pin-to-Pin Compatible with ML4800, FAN4800,

CM6800, and CM6800A

 PWM Configurable for Current-Mode or

Feed-Forward Voltage-Mode Operation

 Internally Synchronized Leading-Edge PFC and

Trailing-Edge PWM in One IC

 Low Operating Current

 Innovative Switching-Charge Multiplier Divider

 Average-Current-Mode for Input-Current Shaping

 PFC Over-Voltage and Under-Voltage Protections

 PFC Feedback Open-Loop Protection

 Cycle-by-Cycle Current Limiting for PFC/PWM

 Power-on Sequence Control and Soft-Start

 Line Sagging Protection

 fRTCT=4•fPFC=4•fPWM for FAN4800AU

 fRTCT=4•fPFC=2•fPWM for FAN4800CU

Applications

 Desktop PC Power Supply

 Internet Server Power Supply

 LCD TV/ Monitor Power Supply

 UPS

 Battery Charger

 DC Motor Power Supply

 Monitor Power Supply

 Telecom System Power Supply

 Distributed Power

Description

The highly integrated FAN4800AU/CU parts are

specially designed for power supplies that consist of

boost PFC and PWM. They require very few external

components to achieve versatile protections and

compensation. They are available in 16-pin DIP and

SOP packages.

The PWM can be used in current or Voltage Mode. In

Voltage Mode, feed-forward from the PFC output bus

can reduce secondary output ripple.

To evaluate FAN4800AU/CU for replacing existing

FAN4800A/C, FAN4800AS/CS, old version FAN4800

and ML4800 boards, six things must be completed

before the fine-tuning procedure:

1. Change RAC resistor from the old value to a higher

resistor value: 6M to 8M.

2. Change RT/CT pin from the existing values to

RT=6.8K and CT=1000pF to have fPFC=64kHz and

fPWM=64kHz.

3. The VRMS pin needs to be 1.224V at VIN=85VAC for

universal input application with line input from

85VAC to 270 VAC.

4. Change ISENSE pin filter from the exiting values to

RFilter=51 and CFilter=0.01µF for higher bandwidth.

5. At full load, the average VVEA must be ~4.5V and

ripple on VVEA needs to be less than 400mV.

6. For the SS pin, the soft-start current has been

reduced to half the FAN4800 capacitor.

There are two differences from FAN4800AS/CS to

FAN4800AU/CU:

 Add Line Sagging Protection

 Fix Inductance Current Instability during AC Cycle

Drop Test

Related Resources

 AN-8027 — FAN480X PFC+PWM Combination

Controller Application

© 2011 Fairchild Semiconductor Corporation

FAN4800AU/CU • Rev. 1.0.0

www.fairchildsemi.com

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