al8807 Diodes, Inc., al8807 Datasheet - Page 13

• Manufacturer Part Number: al8807
• Description: High Efficiency Low Emi 30v 1a Buck Led Driver
• Manufacturer: Diodes, Inc.

Applicatio
EMI and Lay
The AL8807 is
be taken with
radiated emiss
to get the right
edge) dominat
PCB tracks. A
a resonant loo
The tracks from
C1 should be
For PCB track
handling 1A in
inductance. T
effective capac
should be less
AL8807
Document Numbe
ons Informa
yout Conside
After the Schott
ks a figure of 0
s than 5nH.
s a switching re
sions by contro
m the SW pin t
ncreasing the
The resonant
tes the radiate
t compromise
citance of the
r: DS35281 Rev. 3
p between the
as short as po
decoupling an
ossible. There
erations
olling the switch
nd layout of th
3 - 2
ation
to the Anode o
egulator with fa
tky diode rever
d EMI which is
.5nH per mm c
frequency of a
between powe
thickness will
Schottky diode
Schottky diode
(cont.
Place D
Inducto
minimiz
of the Schottky
he PCB.To hel
er dissipation d
or as close as possible
hing speeds of
s due to an int
D1 anode , SW pin and
ze ringing
F
Fig. 36 Reco
ast edges and
rse recovery tim
e capacitance
can be used to
any oscillation
e. An exampl
)
have a minor
is an inductan
Fig. 35 PC
HIGH E
ww
due to switching
CB Loop Res
o estimate the
ww.diodes.com
f the internal po
me of around 5
FFICIENCY
eraction betwe
and the track in
e of good layo
p with these e
ce internally in
mmended P
diode, D1, and
to
measures sm
effect on the
is determined
13 of 20
SW
VIN
GN
sonance
n the AL8807 th
een the Schottk
out is shown in
Y LOW EM
d then from D1
effects the AL8
5ns has occurr
d by the comb
ower MOSFET
all differential v
g losses and r
nductance, L
D
CB Layout
primary resona
inductance an
SET
CTRL
MI 30V 1A B
TR
T. The rise and
nd length will d
radiated EMI.
red; the falling
n figure 36 - th
RACK
8807 has been
ant frequency.
bined inductan
voltages; as a
ky diode (D1),
his can be ass
’s cathode to t
, See figur
BUCK LED
sumed to be ar
nce in the trac
he stray track i
d fall times are
re 35.
n developed to
dominate the s
The turn-on ed
edge of the SW
he decoupling
result of this c
Switching MO
If the track is
AL
© Diodes
Nove
L8807
OSFET and
e controlled
care has to
W pin sees
round 1nH.
ck and the
o minimise
dge (falling
size of the
inductance
mber 2011
s Incorporated
capable of
DRIVER
capacitors