L4984D STMicroelectronics, L4984D Datasheet - Page 24

• Manufacturer Part Number: L4984D
• Description: Power Factor Correction ICs Current Mode PFC CCM Line Modulated Bi
• Manufacturer: STMicroelectronics

Specifications of L4984D

• Rohs: yes

Voltage feedforward
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both surges and drops. A capacitor C
ground, complete an internal peak-holding circuit that provides a DC voltage equal to the
peak of the voltage applied on the MULT pin. In this way, in case of sudden line voltage rise,
C
voltage drop, an internal “mains drop” detector enables a low impedance switch that
suddenly discharges C
voltage level. The discharge of C
the MULT pin or the voltage on the VFF pin falls below 0.88 V, to prevent the “brownout
protection” function from being improperly activated (see
and housekeeping functions
the VFF voltage (and, then, low current distortion) can be achieved with a limited undershoot
or overshoot on the pre-regulator output during line transients.
The twice-mains-frequency (2
peak amplitude that, with good approximation, is given by:
Equation 13
where fL is the line frequency. The amount of 3rd harmonic distortion introduced by this
ripple, related to the amplitude of its 2
Equation 14
Figure 32
amount of maximum desired 3rd harmonic distortion. Note, however, that there is a
minimum value for the time constant R
fast discharge may occur. In fact, the twice-mains-frequency ripple across C
steady-state conditions must be lower than the minimum line drop detection threshold
(ΔV
Equation 15
Always connect R
floating or may be damaged if connected directly to ground.
FF
VFF_min
is rapidly charged through the low impedance of the internal diode; in case of line
shows a diagram that helps choose the time constant R
= 40 mV). Therefore:
FF
and C
FF
, therefore reducing the settling time needed to reach the new
FF
). With this functionality, an acceptably low steady-state ripple of
to the pin; the IC does not work properly if the pin is left
Doc ID 023489 Rev 3
⋅
R
fL) ripple appearing across C
FF
FF
Δ
D
⋅
is stopped when either its voltage equals the voltage on
V
C
3
FF
FF
FF
%
⋅
FF
fL component, is:
and a resistor R
=
>
·C
=
1
FF
2
2
+
π
2
V
below which improper activation of the VFF
f 4
Δ
f
MULTpk
V
L
100
V
L
R
f 4
MULTpk
R
VFF
FF
L
FF
_
C
_
_
C
min
min
max
FF
FF
FF
Section 12: Power management
, connected from the VFF pin to
−
1
FF
is triangular with peak-to-
FF
·C
FF
based on the
FF
under
L4984