lt3479efe-trpbf Linear Technology Corporation, lt3479efe-trpbf Datasheet - Page 6

• Manufacturer Part Number: lt3479efe-trpbf
• Description: 3a, Full Featured Dc/dc Converter With Soft-start And Inrush Current Protection
• Manufacturer: Linear Technology Corporation

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
Taiyo Yuden
AVX
Murata
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 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 I
will suffice 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
LT3479
6
2
Table 2. Suggested Inductors
MANUFACTURER
PART NUMBER
CDRH6D283R0
CDRH6D28100
CDRH4D284R7
LM N 05D B4R7M
LM N 05D B100K
LQH55DN4R7M01L
LQH55DN100M01K
FDV0630-4R7M
R power losses. A 4.7µH or 10µH inductor
U
PHONE
[phone]
[phone]
[phone]
U
W
1.32
1.7
2.2
1.6
2.7
1.7
4.2
I
(A)
DC
3
WEB
www.t-yuden.com
www.avxcorp.com
www.murata.com
U
INDUCTANCE
(µH)
4.7
4.7
4.7
4.7
10
10
10
3
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.
Physically larger inductors provide better efficiency than
smaller ones. Figure 1 shows a 3% to 4% efficiency gain
in using a larger inductor in a 1MHz, 5V to 12V application.
The efficiency 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 efficiency of 85% in an iden-
tical application. Thus, if board space is abundant, then
larger inductors should be used to maximize efficiency.
MAX DCR
(mΩ)
130
24
65
72
49
10
57
49
60
55
50
90
85
80
75
70
65
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
Figure 1. Efficiency vs Inductor Size
0
L × W × H
(mm)
SUMIDA CDRH4D28-4R7
TOKO FDV0630-4R7
0.2
I
OUT
MANUFACTURER
Sumida
www.sumida.com
Taiyo Yuden
www.t-yuden.com
Murata
www.murata.com
Toko
www.toko.com
0.4
(A)
0.6
3479 F01
0.8
3479fa