LTC3455_15 Datasheet, PDF (17/28 Pages) Linear Technology – Dual DC/DC Converter with USB Power Manager and Li-Ion Battery Charger

LTC3455/LTC3455-1
APPLICATIONS INFORMATION
Switching Regulator Inductor Selection
Many different sizes and shapes of inductors are avail-
able from numerous manufacturers. Choosing the right
inductor from such a large selection of devices can be
overwhelming, but following a few basic guidelines will
make the selection process much simpler. To maximize
efficiency, 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/LTC3455-1. These inductors offer a good com-
promise in current rating, DCR and physical size. Consult
each manufacturer for detailed information on their entire
selection of inductors.
Table 1. Recommended Inductors
Inductor
Type
Max Max
L IDC DCR
(μH) (A) (Ω)
DB318C
4.7 0.86 0.1
10 0.58 0.18
CLS4D09 4.7 0.75 0.19
10 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 capacitors
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 tem-
perature 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 manufacturers now
offer very thin (<1mm tall) ceramic capacitors 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 type 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 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 con-
nected to V_MAX to act as a reservoir when the LTC3455/
LTC3455-1 are 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.
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