Data Sheet

© 2012 Fairchild Semiconductor Corporation www.fairchildsemi.com
FLS0116 • Rev. 1.0.2 7
FLS0116 — MOSFET Integrated Smart LED Lamp Driver IC with PFC Function
Dimming Function
The FLS0116 uses the ADIM pin for analog or 0 V to
10 V dimming by using a resistive divider. The peak
voltage of internal reference, which is DAC_OUT signal
in Figure 5, is changed by the V
ADIM
level, as shown in
Figure 7, and has different peak level according to the
operating mode.
Figure 7. V
ADIM
vs. V
DAC_OUT(peak)
Inductor Design
The fixed internal duty ratio range is below 50%, or
around 400 ns, from a timing point of view. The range is
dependent on the input voltage and number of LEDs in
its string.
Minimum duty is calculated as:
(max)
min
in
f
V
Vn
D




(1)
where:
η = efficiency of system;
V
IN(max)
= maximum input voltage;
V
f
= forward drop voltage of LED; and
n = LED number in series connection.
Average
LED Current
Current Limit
t
on
t
off
D
min
1-D
min
∆i
rip
(a) DCM Mode
(b) CCM Mode
t
on
t
off
D
min
1-D
min
∆ i
DCM
DCM
CCM
0.5 ∆ i
0.5 ∆ i
Current peak at LED current
maximum point (I
LED(peak)
)
Current min at LED current
maximum point (I
LED(min)
)
Average
LED Current (I
LED(ave)
)
Current peak at LED average
current maximum point
(I
LED(ave.peak)
)
Figure 8. DCM and CCM Operation
In DCM Mode, inductance is:
][
)1(
min
H
if
DVn
L
rips
f
m



(2)
If the peak current is fixed at 350 mApk, the
formula for the peak current is:
2
).(
rip
conpeaka veLED
i
iI


[A]
(3)
In FL7701, the LED RMS current determines the
inductance parameter. To drive for CCM Mode, define
LED RMS current first, as:
2
).(
)(
peakaveLED
rmsLED
I
I 
[A]
(4)
Substituting Equation (2) for Equation (4), the
inductance of inductor is obtained.
V
bridge
V
drain
I
LED
V
IN
V
LED
DAC
I
FRD
I
MOSFET
I
input
T/2 = 1/(Input Frequency * 2)
T = 1/Input Ferquency
V
DD
Charging
Voltage
Bridge Diode
Output Voltage
Input Voltage
Peak
ZCD
Π
2Π
3Π
4Π
Input Voltage
Peak
Input Voltage
Peak
t
t
t
t
t
t
t
t
t
t
Figure 9. Typical Performance Characteristics
V
ADIM
V
DAC
_
OUT
AC Mode
DC Mode
0
.
5
V
0
.
365
V
3
.
5
V
0
.
5
V