LTC3400-1
APPLICATIO S I FOR ATIO
The inductor current ripple is typically set for 20% to 40%
of the maximum inductor current (I
P
). High frequency
ferrite core inductor materials reduce frequency depen-
dent power losses compared to cheaper powdered iron
types, improving efficiency. The inductor should have low
ESR (series resistance of the windings) to reduce the I
2
R
power losses, and must be able to handle the peak
inductor current without saturating. Molded chokes and
some chip inductors usually do not have enough core to
support the peak inductor currents of 850mA seen on the
LTC3400-1. To minimize radiated noise, use a toroid, pot
core or shielded bobbin inductor. See Table 1 for some
suggested components and suppliers.
Table 1. Recommended Inductors
L
(µH)
4.1
10
4.7
4.7
10
4.7
3.3
4.7
10
4.7
4.7
10
4.7
MAX
DCR
mΩ
57
124
105
170
109
182
216
174
60
75
90
84
137
195
HEIGHT
(mm)
2.0
2.0
1.8
1.8
3.5
3.5
0.8
0.8
2.9
2.9
2.9
2.0
2.0
2.2
PART
CDRH5D18-4R1
CDRH5D18-100
CDRH3D16-4R7
CDRH3D16-6R8
CR43-4R7
CR43-100
CMD4D06-4R7MC
CMD4D06-3R3MC
DS1608-472
DS1608-103
DO1608C-472
D52LC-4R7M
D52LC-100M
LQH3C4R7M24
VENDOR
Sumida
(847) 956-0666
www.sumida.com
Coilcraft
(847) 639-6400
www.coilcraft.com
Toko
(408) 432-8282
www.tokoam.com
Murata
www.murata.com
Output and Input Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used to minimize the output voltage ripple. Multilayer
ceramic capacitors are an excellent choice as they have
U
extremely low ESR and are available in small footprints. A
2.2µF to 10µF output capacitor is sufficient for most
applications. Larger values up to 22µF may be used to
obtain extremely low output voltage ripple and improve
transient response. An additional phase lead capacitor
may be required with output capacitors larger than 10µF
to maintain acceptable phase margin. X5R and X7R
dielectric materials are preferred for their ability to main-
tain capacitance over wide voltage and temperature ranges.
Low ESR input capacitors reduce input switching noise
and reduce the peak current drawn from the battery. It
follows that ceramic capacitors are also a good choice for
input decoupling and should be located as close as pos-
sible to the device. A 4.7µF input capacitor is sufficient for
virtually any application. Larger values may be used with-
out limitations. Table 2 shows a list of several ceramic
capacitor manufacturers. Consult the manufacturers di-
rectly for detailed information on their entire selection of
ceramic parts.
Table 2. Capacitor Vendor Information
SUPPLIER
AVX
Murata
Taiyo Yuden
PHONE
(803) 448-9411
(714) 852-2001
(408) 573-4150
WEBSITE
www.avxcorp.com
www.murata.com
www.t-yuden.com
W
U U
Output Diode
Use a Schottky diode such as an MBR0520L, PMEG2010EA,
1N5817 or equivalent if the converter output voltage is 4.5V
or greater. The Schottky diode carries the output current for
the time it takes for the synchronous rectifier to turn on. Do
not use ordinary rectifier diodes, since the slow recovery
times will compromise efficiency. A Schottky diode is also
strongly recommended for output voltages below 4.5V,
and will increase converter efficiency by 2% to 3%.
34001f
7
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