LTC3456 Datasheet, PDF (20/28 Pages) Linear Technology – 2-Cell, Multi-Output DC/DC Converter with USB Power Manager

LTC3456
APPLICATIO S I FOR ATIO
COMPONENT SELECTION
Inductor Selection
The high frequency operation of LTC3456 allows the use
of small surface mount inductors. For most applications,
the inductance value will be between 2.2µH and 10µH. The
desired value of inductance is determined by the amount
of ripple current, ∆I_L, in the converter.
The inductor current ripple, ∆I_L, for Boost mode operation
neglecting the voltage drop across the switches is given
by:
( ) _∆IL
=
V_IN • V_OUT – V_IN
V_OUT • f • L
The inductor current ripple, ∆I_L, for Buck mode operation
neglecting the voltage drop across the switches is given
by:
( ) _∆IL1
=
V_OUT
• V_IN
V_IN • f
– V_OUT
•L
where
L = Inductor
f = Operating Frequency
V_IN = Input Voltage
V_OUT = Output Voltage
The ∆I_L is typically set to 20% to 40% of the maximum
inductor current.
The inductor should have a saturation current rating
greater than the peak inductor current required for the
application. Also, ensure that the inductor has a low DCR
(copper wire resistance) to minimize I²R power losses.
Several inductors that work well with the LT3456 are listed
in Table 1. Consult each manufacturer for more detailed
information and for their entire selection of related parts.
Table 1. Recommended Inductors
PART
MAX CURRENT
L DCR RATING
(µH) (Ω)
(mA)
ELT5KT-4R7
ELT5KT-100
4.7 0.2
950
10 0.36
680
CDRH4D18-4R7 4.7 0.16
840
CDRH4D18-100
10
0.2
610
LQH32CN4R7
LQH32CN100
4.7 0.15
650
10 0.3
450
1002AS-4R7M
1002AS-100M
4.7 0.19
910
10 0.32
620
VENDOR
Panasonic
[phone]
www.panasonic.com
Sumida
[phone]
www.sumida.com
Murata
[phone]
www.murata.com
Toko
[phone]
www.toko.com
Output Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used at the output to minimize the output ripple voltage.
Multilayer ceramic capacitors are an excellent choice, as
they have an extremely low ESR and are available in very
small packages. Use only X7R or X5R dielectrics, as these
materials retain their capacitance over wider voltage and
temperature ranges than other dielectrics. A 1µF to 22µF
output capacitor is sufficient for most applications. Solid
tantalum or OS-CON capacitors can be used, but they will
occupy more board area than a ceramic and will have a
higher ESR for the same device footprint. Always use a
capacitor with a sufficient voltage rating.
Table 2 shows a list of several ceramic capacitor manufac-
turers. Consult the manufacturers for detailed information
on their entire selection of ceramic parts.
Table 2. Ceramic Capacitor Manufacturers
Taiyo Yuden
[phone]
www.t-yuden.com
AVX
[phone]
www.avxcorp.com
Murata
[phone]
www.murata.com
TDK
[phone]
www.component.tdk.com
3456fa
20