Diodes AL8808 - Manual (Page 18)

NEW PROD
UC
T
AL8808
Document number
Applicatio
Fault Conditio
The AL8808 has
V
IN
and the SW
If the LEDs shou
the expected cu
dramatically and
LEDs.
The on-time of t
inductor. The off
32) causing a m
High Tempera
The AL8808 is a
temperature in
temperatures an
AL8808 off. This
The OTP shutdo
never switch-off
junction tempera
r: DS35648 Rev. 2
on Informat
on Operation
s by default open
pin will then fall
uld become shor
urrent - so no e
d the switching f
the internal pow
f-time is significa
uch slower deca
ature Operatio
a high efficiency
excess of 100°
nd hence junctio
s will allow the ju
own junction tem
with a junction t
ature of the AL88
- 2
tion
(cont.)
n LED protection
to GND. No exce
rted together the
excessive heat w
requency will mo
er MOSFET swi
antly increased b
ay in inductor cur
Figure 45. Sw
on and Protec
switching LED d
C given the co
on temperature t
nction temperatu
mperature of the
temperature belo
808.
w
n. If the LEDs sh
essive voltages w
AL8808 will con
will be generated
ost likely decrea
itch is significant
ecause the reve
rrent.
witching Charac
tion
river capable of
orrect thermal im
then the Over-Te
ure of the AL880
e AL8808 is app
ow +125°C allow
18 of 20
www.diodes.co
hould become op
will be seen by th
ntinue to switch a
d within the AL8
se. See Figure 4
tly reduced beca
rse voltage acros
cteristics (norma
operating junctio
mpedance to fre
emperature Prot
8 to cool down a
roximately +145
wing the designe
m
pen circuit the AL
he AL8808.
and the current t
8808. However,
45 for an examp
ause almost all o
ss the inductor is
al open to short
on temperatures
ee air. If a fault
tection (OTP) of
and potentially giv
°C with a hyster
r to design the s
L8808 will stop o
hrough the AL88
the duty cycle
ple of this behav
of the input volta
s now just the Sc
t LED chain)
up to +125°C. T
should occur t
f the AL8808 wil
ving an opportun
resis of +10°C.
system thermally
oscillating; the SE
808’s internal sw
at which it oper
ior at 24V input
age is now deve
chottky diode vol
his allows it ope
that leads to inc
ll cut in turning t
nity for the fault to
This means that
to fully utilize th
January 201
© Diodes Incorporate
AL8808
ET pin will rise to
witch will still be a
rates will change
voltage driving 3
eloped across the
ltage (See Figure
rate with ambien
creased ambien
the output of the
o clear itself.
t the AL8808 wi
he wide operating
3
ed
o
at
e
3
e
e
nt
nt
e
ll
g