Datasheet

LT3477
8
3477fc
APPLICATIONS INFORMATION
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 suffi cient 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 [phone] www.t-yuden.com
AVX [phone] www.avxcorp.com
Murata [phone] www.murata.com
TDK [phone] 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 effi ciency. 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 I
2
R power losses. A 4.7μH or 10μH inductor
will suffi ce 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 rat-
ing of the inductor to save board space. Consult each
manufacturer 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 exceed
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 suffi cient for
most designs. The companies below also offer Schottky
diodes with higher voltage and current ratings.
Table 3. Suggested Diodes
MANUFACTURER
PART NUMBER
MAX
CURRENT (A)
MAX REVERSE
VOLTAGE (V) MANUFACTURER
UPS340
UPS315
3
3
40
15
Microsemi
www.microsemi.com
B220
B230
B240
B320
B330
B340
SBM340
2
2
2
3
3
3
3
20
30
40
20
30
40
40
Diodes, Inc
www.diodes.com
Table 2. Suggested Inductors
MANUFACTURER
PART NUMBER
I
DC
(A)
INDUCTANCE
(μH)
MAX DCR
(mΩ)
L × W × H
(mm)
MANUFACTURER
CDRH6D283R0
CDRH6D28100
CDRH4D284R7
3
1.7
1.32
3
10
4.7
24
65
72
6.7 × 6.7 × 3.0
6.7 × 6.7 × 3.0
5.0 × 5.0 × 3.0
Sumida
www.sumida.com
LM N 05D B4R7M
LM N 05D B100K
2.2
1.6
4.7
10
49
10
5.9 × 6.1 × 2.8
5.9 × 6.1 × 2.8
Taiyo Yuden
www.t-yuden.com
LQH55DN4R7M01L
LQH55DN100M01K
2.7
1.7
4.7
10
57
130
5.7 × 5.0 × 4.7
5.7 × 5.0 × 4.7
Murata
www.murata.com
FDV0630-4R7M 4.2 4.7 49
7.0 × 7.7 × 3.0
Toko
www.toko.com