The L4984D is a current-mode PFC controller operating with line-modulated fixed-off-time
(LM-FOT) control. A proprietary LM-FOT modulator allows fixed-frequency operation for
boost PFC converters as long as they are operated in CCM (continuous conduction mode).
The chip comes in a 10-pin SO package and offers a low-cost solution for CCM-operated
boost PFC pre-regulators in EN61000-3-2 and JEIDA-MITI compliant applications, in a
power range that spans from few hundred W to 1 KW and above.
The highly linear multiplier includes a special circuit, able to reduce the crossover distortion
of the AC input current, that allows wide-range-mains operation with a reasonably low THD,
even over a large load range.
The output voltage is controlled by means of a voltage-mode error amplifier and an accurate
(1% at Tj = 25 °C) internal voltage reference. Loop stability is optimized by the voltage
feedforward function (1/V2 correction), which in this IC uses a proprietary technique that
also significantly improves line transient response in the case of mains drops and surges
The device features low consumption and includes a disable function suitable for IC remote
on/off. These features allow use in applications which also comply with the latest energy
saving requirements (Blue Angel, ENERGY STAR®, Energy 2000, etc.).
In addition to overvoltage protection able to keep the output voltage under control during
transient conditions, the IC is also provided with protection against feedback loop failures or
erroneous settings. Other onboard protection functions allow that brownout conditions and
boost inductor saturation can be safely handled. Soft-start limits peak current and extends
off-time to prevent flux runaway in the initial cycles.
The totem pole output stage, capable of 600 mA source and 800 mA sink current, is suitable
for big MOSFETs or IGBT drive.
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