FAN4800AS: CCM PFC + PWM Combination Controller with Surge Capability Enhancement

The highly integrated FAN4800AS/CS/01S/02S parts are specially designed for power supplies that consist of boost PFC and PWM. They require very few external components to achieve versatile protections / compensation. They are available in 16-pin DIP and SOP packages.

The PWM can be used in either current or voltage mode. In voltage mode, feed-forward from the PFC output bus can reduce the secondary output ripple.

Compared with older productions, ML4800 and FAN4800, FAN4800AS/CS/01S/02S have lower operation current that saves power consumption in external devices. FAN4800AS/CS/01S/02S have accurate 49.9% maximum duty of PWM that makes the hold-up time longer. Brownout protection and PFC soft-start functions available in this series are not available in ML4800 and FAN4800.

To evaluate FAN4800AS/CS/01S/02S for replacing existing FAN4800 and ML4800 boards, five things must be completed before the fine-tuning procedure:

1. Change RAC resister from the old value to a higher resister: between 6 MΩ to 8 MΩ.

2. Change RT/CT pin from the existing values to RT=6.8 kΩ and CT=1000 pF to have fPFC=64 kHz and fPWM=64 kHz.

3. The VRMS pin needs to be 1.224 V at VIN=85 VAC for universal input application from line input from 85 VAC to 270 VAC.

4. At full load, the average VVEA needs to be ~4.5 V and the ripple of VVEA needs to be less than 400 mV.

5. For the Soft-Start pin, the soft-start current has been reduced to half the FAN4800 capacitor.

There are two differences from FAN4800A/C/01/02 to FAN4800AS/CS/01S/02S:

1. Under-voltage protection debounce time is extended to one second.

2. PWM gate clamp voltage is raised to 19 V.

Features

• Pin-to-Pin Compatible with ML4800 and FAN4800 and CM6800 and CM6800A
• PWM Configurable for Current Mode or Feedforward 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
• Brownout Protection
• Interleaved PFC/PWM Switching
• Improved Efficiency at Light Load
• f_RTCT=4xf_PFC=4xf_PWM for FAN4800AS/01S
• f_RTCT=4xf_PFC=2xf_PWM for FAN4800CS/02S

Application Notes