L6563STR View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6563STR' PDF : 43 Pages View PDF
Application information
L6563S
The twice-mains-frequency (2•fL) ripple appearing across CFF is triangular with a peak-to-
peak amplitude that, with good approximation, is given by:
ΔVFF
=
2 VMULTpk
1+ 4fLRFFCFF
where fL is the line frequency. The amount of 3rd harmonic distortion introduced by this
ripple, related to the amplitude of its 2•fL component, will be:
D3 %
=
100
2π fLRFFCFF
Figure 37 shows a diagram that helps choose the time constant RFF·CFF based on the
amount of maximum desired 3rd harmonic distortion. Note that there is a minimum value for
the time constant RFF • CFF below which improper activation of the VFF fast discharge may
occur. In fact, the twice-mains-frequency ripple across CFF under steady state conditions
must be lower than the minimum line drop detection threshold (VVFF_min = 40 mV).
Therefore:
2 VMULTpk _ max − 1
RFF ⋅ CFF >
ΔVVFF _ min
4 fL _ min
Always connect RFF and CFF to the pin, the IC will not work properly if the pin is either left
floating or connected directly to ground.
Figure 37. RFF·CFF as a function of 3rd harmonic distortion introduced in the input
current
10
1
RFF · CFF [s]
0.1
0.01
0.1
f L= 50 Hz
f L= 60 Hz
1
10
D3 %
26/43
Doc ID 16116 Rev 4
Share Link: 
