ltc3455euf-trpbf Linear Technology Corporation, ltc3455euf-trpbf Datasheet - Page 17

• Manufacturer Part Number: ltc3455euf-trpbf
• Description: Dual Dc/dc Converter With Usb Power Manager And Li-ion Battery Charger
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Switching Regulator Inductor Selection
Many different sizes and shapes of inductors are available
from numerous manufacturers. Choosing the right induc-
tor from such a large selection of devices can be over-
whelming, but following a few basic guidelines will make
the selection process much simpler. To maximize effi-
ciency, choose an inductor with a low DC resistance. Keep
in mind that most inductors that are very thin or have a very
small volume typically have much higher core and DCR
losses, and will not give the best efficiency.
Choose an inductor with a DC current rating at least 1.5
times larger than the maximum load current to ensure that
the inductor does not saturate during normal operation.
Table 1 shows several inductors that work well with the
LTC3455. These inductors offer a good compromise in
current rating, DCR and physical size. Consult each manu-
facturer for detailed information on their entire selection of
inductors.
Table 1. Recommended Inductors
CDRH3D16
CLS4D09
Inductor
DB318C
ELT5KT
SD12
Type
(µH)
4.7
4.7
4.7
4.7
4.7
10
10
10
10
10
L
U
Max
0.86
0.58
0.75
0.55
1.29
0.82
0.68
I
(A)
0.5
0.9
DC
1
U
Max
DCR
0.18
0.19
0.37
0.11
0.21
0.12
0.28
0.36
(Ω)
0.1
0.2
Height
(mm)
1.8
1.8
1.8
1.8
1.2
1.2
1.2
1.2
1
1
W
www.panasonic.com
www.cooperet.com
www.sumida.com
[phone]
www.toko.com
[phone]
[phone]
[phone]
Manufacturer
Panasonic
Sumida
Sumida
Cooper
Toko
U
Switching Regulator Output Capacitor Selection
Low ESR (equivalent series resistance) ceramic capaci-
tors should be used at both switching regulator outputs.
Only X5R or X7R ceramic capacitors should be used
because they retain their capacitance over wider voltage
and temperature ranges than other ceramic types. A 10µF
output capacitor is sufficient for most applications. Table
2 shows a list of several ceramic capacitor manufacturers.
Consult each manufacturer for detailed information on
their entire selection of ceramic capacitors. Many manu-
facturers now offer very thin (<1mm tall) ceramic capaci-
tors ideal for use in height-restricted designs.
Table 2. Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden
AVX
Murata
TDK
V
For the V
best choice. Only X5R or X7R type ceramic capacitors
should be used.
V
For the V
choice. Only X5R or X7R type ceramic capacitors should
be used. Do not use less than 10µF on this pin. For some
designs it may be desirable to use a larger capacitor
connected to V
is USB powered. Up to 50µF of ceramic capacitance may
be connected to the V
50µF requires using a capacitor with some ESR (like a
Tantalum or OS-CON) or adding some resistance in series
with some of the ceramic capacitance. This is necessary
to ensure loop stability in the battery charger loop when
under USB power.
BAT
MAX
Pin Capacitor Selection
Pin Capacitor Selection
BAT
MAX
pin, a 4.7µF to 10µF ceramic capacitor is the
pin, a 10µF ceramic capacitor is the best
MAX
to act as a reservoir when the LTC3455
[phone]
[phone]
[phone]
[phone]
MAX
pin without difficulty. More than
LTC3455
www.avxcorp.com
www.t-yuden.com
www.murata.com
www.tdk.com
17
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