The highly integrated FAN4800A/C and FAN4801/1S/2/2L 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, FAN4800A/C and
FAN4801/1S/2/2L have lower operation current that save power consumption in
external devices. FAN4800A/C and FAN4801/1S/2/2L have accurate 49.9% maximum
duty of PWM that makes the hold-up time longer. Specifically, the brownout
protection and PFC soft-start functions are not in ML4800 and FAN4800.
To start evaluating FAN4800A/C, FAN4801/1S/2/2L for replacing existing
FAN4800 and ML4800 boards, five things must be done before the fine-tuning
procedure:
1. Change RAC resister from the old value to a higher resister:
between 6MW to 8MW.
2. Change RT/CT pin from the existing values to RT=6.8KWand CT=1000pF to have fPFC=64KHz,
fPWM=64KHz.
3. VRMS pin needs to be 1.224V at VIN=85 VAC for
universal input application from line input from 85VAC to 270
VAC. Both poles for the Vrms of FAN4801/1S/2/2L don’t need
to substantially slower than FAN4800; about 5 to 10 times.
4. At full load, the average VEA needs to ~4.5V and the ripple on
the VEA needs to be less than 400mV.
5. Soft-Start pin, the soft-start current has been reduced to half from the
FAN4800 capacitor.
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