LT3479 Просмотр технического описания (PDF) - Linear Technology
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LT3479
Linear Technology
LT3479 Datasheet PDF : 20 Pages
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LT3479
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 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
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 I2R power losses. A 4.7μH or 10μH inductor
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 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 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 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 identical
application. Thus, if board space is abundant, then larger
inductors should be used to maximize efficiency.
90
85
80
TOKO FDV0630-4R7
75
SUMIDA CDRH4D28-4R7
70
65
60
55
50
0
0.2
0.4
0.6
0.8
IOUT (A)
3479 F01
Figure 1. Efficiency vs Inductor Size
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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