LT3477E Ver la hoja de datos (PDF) - Linear Technology
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LT3477E Datasheet PDF : 20 Pages
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LT3477
APPLICATIO S I FOR ATIO
Capacitor Selection
Low ESR (equivalent series resistance) ceramic capaci-
tors should be used at the output to minimize the output
ripple voltage. Use only X5R or X7R dielectrics, as these
materials retain their capacitance over wider voltage and
temperature ranges better than other dielectrics. A 4.7µF
to 10µF output capacitor is sufficient for most high output
current designs. Converters with lower output currents
may need only a 1µF or 2.2µF output capacitor.
Table 1. Ceramic Capacitor Manufacturers
MANUFACTURER PHONE
WEB
Taiyo Yuden
(408) 573-4150
www.t-yuden.com
AVX
(803) 448-9411
www.avxcorp.com
Murata
(714) 852-2001
www.murata.com
TDK
(847) 803-6100
www.component.tdk.com
Inductor Selection
Several inductors that work well with the LT3477 are listed
in Table 2. However, there are many other manufacturers
and devices that can be used. Consult each manufacturer
for more detailed information and their entire range of
parts. Ferrite core inductors should be used to obtain the
best efficiency. Choose an inductor that can handle the
necessary peak current without saturating, and ensure
that the inductor has a low DCR (copper-wire resistance)
to minimize I2R power losses. A 4.7µH or 10µH inductor
will suffice for most LT3477 applications.
Inductor manufacturers specify the maximum current
rating as the current where the inductance falls to some
percentage of its nominal value—typically 65%. An
inductor can pass a current larger than its rated value
without damaging it. Aggressive designs where board
space is precious will exceed the maximum current rating
of the inductor to save board space. Consult each manu-
facturer to determine how the maximum inductor current
is measured and how much more current the inductor can
reliably conduct.
Diode Selection
Schottky diodes, with their low forward voltage drop and
fast switching speed, are ideal for LT3477 applications.
Table 3 lists several Schottky diodes that work well with
the LT3477. The diode’s average current rating must ex-
ceed the average output current. The diode’s maximum
reverse voltage must exceed the output voltage. The diode
conducts current only when the power switch is turned off
(typically less than 50% duty cycle), so a 3A diode is suf-
ficient for most designs. The companies below also offer
Schottky diodes with higher voltage and current ratings.
Table 3. Suggested Diodes
MANUFACTURER MAX MAX REVERSE
PART NUMBER CURRENT (A) VOLTAGE (V) MANUFACTURER
UPS340
UPS315
3
40
Microsemi
3
15
www.microsemi.com
B220
B230
B240
B320
B330
B340
SBM340
2
20
Diodes, Inc
2
30
www.diodes.com
2
40
3
20
3
30
3
40
3
40
Table 2. Suggested Inductors
MANUFACTURER
IDC
PART NUMBER
(A)
CDRH6D283R0
3
CDRH6D28100
1.7
CDRH4D284R7
1.32
LM N 05D B4R7M
2.2
LM N 05D B100K
1.6
LQH55DN4R7M01L
2.7
LQH55DN100M01K
1.7
FDV0630-4R7M
4.2
INDUCTANCE
(µH)
3
10
4.7
4.7
10
4.7
10
4.7
MAX DCR
(mΩ)
24
65
72
49
10
57
130
49
L×W×H
(mm)
6.7 × 6.7 × 3.0
6.7 × 6.7 × 3.0
5.0 × 5.0 × 3.0
5.9 × 6.1 × 2.8
5.9 × 6.1 × 2.8
5.7 × 5.0 × 4.7
5.7 × 5.0 × 4.7
7.0 × 7.7 × 3.0
MANUFACTURER
Sumida
www.sumida.com
Taiyo Yuden
www.t-yuden.com
Murata
www.murata.com
Toko
www.toko.com
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