AL8808WT-7 Diodes Inc., AL8808WT-7 Datasheet - Page 16

• Manufacturer Part Number: AL8808WT-7
• Description: LED Lighting Drivers LED MV Int Switch TS Switch TSOT25 T&R 3K
• Manufacturer: Diodes Inc.

Specifications of AL8808WT-7

• Rohs: yes
• Input Voltage: 6 V to 30 V
• Operating Frequency: 1 MHz
• Maximum Supply Current: 450 uA
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: TSOT-25
• Minimum Operating Temperature: - 40 C

Applicatio
EMI and Layo
The AL8808 is
decoupling and
switching speed
due to switching
The turn-on edg
and PCB tracks
between the Sch
The tracks from
short as possible
There is an indu
estimate the prim
and length will d
The resonant fre
diode. An exam
Summary:
1.
2.
3.
4.
5.
AL8808
Document number
Use a
the gr
(EMC
Place
less th
the in
parasi
more g
Place
Place
Place
capac
imped
on Informat
mple of good layo
out Considerat
ds of the internal
g losses and radia
ge (falling edge)
uctance internally
dominate the size
citor and its copp
dance coupling d
round areas are
hottky diode capa
mary resonant fr
han about 5mm.
r: DS35648 Rev. 2
e.
equency of any
. After the Scho
) operation and a
put current pass
itic inductance of
ground via holes
layout of the PC
a switching reg
capacitor C1 as
sense resistor R
D1 anode, the S
the SW pin to t
PCB constructio
capacitor C2 as
Figure 43. PC
ottky diode revers
R1 as close as po
per trace such tha
ses directly throu
SW pin and the in
CB.To help with
e of the inductanc
CB Loop Reson
s close to the gro
y in the AL8808 t
tion
the Anode of the
on with copper fo
also to minimize
tions
ated EMI.
acitance and the
s close as poss
ulator with fast
equency. If the t
f the copper trac
ue to the added
dominates the ra
ut is shown in Fi
oscillation is det
- 2
tightly connecte
close as possib
power MOSFET
To ensure the b
(cont.)
e track inductanc
ce. Ensure low in
ound pad.
ed together using
ugh the capacito
e Schottky diode
best possible EM
se recovery time
oil on top and bo
ossible to V
nductor as close
this can be assu
ce.
T. The rise and
adiated EMI whi
termined by the
le to V
ible to L1 and S
at the input curre
rack is capable o
ance
edges and mea
these effects the
gure 44 - the str
device temperat
parasitic inducta
IN
, and as
IN
and
MI filtering (greate
ottom. Provide m
d fall times are c
e, D1, and then f
SET. To ensure
ance of the coppe
asures small diff
g plated via hole
tures by spreadin
nductance conne
w
www.diodes.co
e AL8808 has b
of handling 1A in
ent passes direc
ch is due to an i
e, L
ay track inductan
r mounting pad.
d SET.
med to be aroun
close as possib
together as poss
combined induc
of around 5ns h
TRACK
16 of 20
, See F
maximum coverag
controlled to get
e the best possib
ctly through the c
has occurred; the
Figure 43.
nd 1nH. For PCB
ncreasing the thic
est attenuation),
ctance in the tra
es placed at reg
ng the dissipated
ection between th
ferential voltages
from D1’s cathod
nce should be le
er trace.
interaction betwe
le to the cathode
sible to avoid rin
m
een developed t
This minimizes
Figure
d heat.
e of D1. The sep
capacitor mountin
e falling edge of
s common imped
een the Schottky
B tracks a figure
ble EMI filtering
s; as a result of
to minimise radia
de to the decoup
ge of copper gro
he capacitor and
ckness will have
ss than 5nH.
the right compro
ck and the effec
ular intervals. T
place the capaci
ging.
44. Recommen
e a minor effect o
paration of these
omise between p
d its ground conn
y diode (D1), Sw
ctive capacitance
nded PCB Layo
This is required
dance coupling d
pling capacitors
ated emissions b
itor and its coppe
ng pad. This mi
f this care has
und plane on bo
the SW pin sees
of 0.5nH per mm
(greatest attenu
witching MOSFET
oth sides. Ensure
on the inductance
nection. Use 2 o
uation), place the
power dissipation
s a resonant loop
m can be used to
e of the Schottky
er trace such tha
due to the added
by controlling the
to be taken with
ut
both for low EM
nimizes common
C1 should be as
nodes should be
© Diodes Incorporate
AL8808
January 201
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