Diodes AL8808 - Manual (Page 13)

NEW PROD
UC
T
AL8808
Document number
Applicatio
Inductor Sele
Recommended
data for selecte
required switchi
LED current acc
The inductor sho
The chosen coil
required mean o
Suitable coils for
Part
MSS1038-333
MSS1038-683
NPIS64D330M
The inductor val
The following eq
Switch ‘On’ tim
V
t
IN
ON −
=
Switch ‘Off’ tim
V
t
L
OFF
=
Where:
L is the coil
r
L
is the coil
R
S
is the cur
I
avg
is the re
V
IN
is the su
ΔI is the coil
V
LED
is the t
R
SW
is the s
V
D
is the dio
r: DS35648 Rev. 2
on Informat
ection
inductor values
ed component va
ng frequency. L
curacy (due to pro
ould be mounted
should have a s
output current.
r use with the AL
No.
MTRF
ue should be cho
quations can be u
me:
x I V
L
AVG LED
− −
Δ
me:
I V
I L
AVG D LED
+ +
Δ
inductance (H)
resistance (Ω)
rrent sense resis
quired LED curre
upply voltage (V)
l peak-peak rippl
total LED forward
switch resistance
ode forward volta
- 2
tion
(cont.)
for the AL8808
alues. The induc
Lower inductor v
opagation delays
Figure 4
d as close to the d
saturation current
L8807 are listed i
L
(µH)
D
(
33 0.
68 0.
33 0.
osen to maintain
used as a guide,
(
R r R x
I
SW L S
+ +
( )
r R x
L S G
+
stance (Ω)
ent (A)
e current (A) {Int
d voltage (V)
(Ω) {=0.35Ω nom
age at the require
w
are in the range
ctance used will
alues can be us
s) and increase p
0. Inductor Valu
device as possib
t higher than the
in the table below
DCR
(V)
I
SAT
(A)
093 2.3
213 1.5
124 1.1
n operating duty c
with reference t
)
W
ternally set to 0.4
minal}
ed load current (V
13 of 20
www.diodes.co
e 33µH to 100µH
depend on a c
sed to increase t
power dissipation
ue with Input Volt
ble with low resis
peak output cur
w:
T
)
3
Co
5
1
cycle and switch
o Figure 1 - Ope
4 x I
AVG
}
V)
m
H. Note that the
combination of In
he switching freq
n (due to switchin
tage and Numbe
stance/stray induc
rrent and a contin
Manufactu
oilCraft www.coi
NIC www.niccom
'on'/'off' times ov
erating waveform
Figure
e AL8808 Web C
nput voltage and
quency and redu
ng losses).
er of LEDs
ctance connectio
nuous current rat
rer
lcraft.com
mp.com
ver the supply vo
ms.
e 41. Typical Swi
Calculator provid
d LED chain vo
uce solution size
ons to the SW pi
ting above the
oltage and load c
itching Waveform
January 201
© Diodes Incorporate
AL8808
es performance
ltage to set the
e but may affect
n.
current range.
m
3
ed