Datasheet

LT3479
8
3479fc
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
Inductor Selection
Several inductors that work well with the LT3479 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 LT3479 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
APPLICATIONS INFORMATION
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
Figure 1. Effi ciency vs Inductor Size
I
OUT
(A)
0
EFFICIENCY (%)
70
80
0.8
3479 F01
60
50
0.2
0.4
0.6
90
65
75
55
85
SUMIDA CDRH4D28-4R7
TOKO FDV0630-4R7
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 manufacturer
to determine how the maximum inductor current is
measured and how much more current the inductor can
reliably conduct.
Physically larger inductors provide better effi ciency than
smaller ones. Figure 1 shows a 3% to 4% effi ciency gain
in using a larger inductor in a 1MHz, 5V to 12V application.
The effi ciency of the TOKO FDV0630-4R7M, which mea-
sures 7mm × 7.7mm and 3 mm thick, peaks at 87%. The
smaller Sumida CDRH4D28-4R7 which is 5mm × 5mm and
3mm thick yields a peak effi ciency of 85% in an identical
application. Thus, if board space is abundant, then larger
inductors should be used to maximize effi ciency.