Datasheet

L6563H Application information
Doc ID 16047 Rev 3 27/49
The twice-mains-frequency (2•f
L
) ripple appearing across C
FF
is triangular with a peak-to-
peak amplitude that, with good approximation, is given by:
where f
L
is the line frequency. The amount of 3rd harmonic distortion introduced by this
ripple, related to the amplitude of its 2
•f
L
component, is:
Figure 40 shows a diagram that helps choose the time constant R
FF
·C
FF
based on the
amount of maximum desired 3rd harmonic distortion.
Note that there is a minimum value for the time constant R
FF
·C
FF
below which improper
activation of the V
FF
fast discharge may occur. In fact, the twice-mains-frequency ripple
across C
FF
under steady state conditions must be lower than the minimum line drop
detection threshold (ΔV
VFF_min
= 40 mV). Therefore:
Always connect R
FF
and C
FF
to the pin, the IC will not work properly if the pin is either left
floating or connected directly to ground.
Figure 40. R
FF
·C
FF
as a function of 3rd harmonic distortion introduced in the input
current
FFFFL
MULTpk
FF
CRf41
V2
V
+
=Δ
FFFFL
3
CRf2
100
%D
π
=
min_L
min_VFF
max_MULTpk
FFFF
f4
1
V
V
2
CR
−
Δ
>⋅

D %
3
0.1110
0.01
0.1
1
10
f = 50 Hz
L
f = 60 Hz
L
R · C [s]
FFFF