LTC3455 Datasheet, PDF (16/24 Pages) Linear Technology – Dual DC/DC Converter with USB Power Manager and Li-Ion Battery Charger

LTC3455
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
Max Max
Inductor L
I_DC DCR
Type (µH) (A) (Ω)
DB318C 4.7 0.86 0.1
10 0.58 0.18
CLS4D09 4.7
10
0.75 0.19
0.5 0.37
CDRH3D16 4.7
10
SD12
4.7
10
0.9 0.11
0.55 0.21
1.29 0.12
0.82 0.28
ELT5KT 4.7
1
0.2
10 0.68 0.36
Height
(mm)
Manufacturer
1.8
Toko
1.8
[phone]
www.toko.com
1
Sumida
1
[phone]
www.sumida.com
1.8
Sumida
1.8
1.2
Cooper
1.2
[phone]
www.cooperet.com
1.2
Panasonic
1.2
[phone]
www.panasonic.com
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
[phone]
www.t-yuden.com
AVX
[phone]
www.avxcorp.com
Murata
[phone]
www.murata.com
TDK
[phone]
www.tdk.com
V_BAT Pin Capacitor Selection
For the V_BAT pin, a 4.7µF to 10µF ceramic capacitor is the
best choice. Only X5R or X7R ceramic capacitors should
be used.
V_MAX Pin Capacitor Selection
For the V_MAX pin, a 10µF ceramic capacitor is the best
choice. Only X5R or X7R 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_MAX to act as a reservoir when the LTC3455
is USB powered. Up to 50µF of ceramic capacitance may
be connected to the V_MAX pin without difficulty. More than
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.
3455f
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