Datasheet

LTC3442
13
3442fa
APPLICATIO S I FOR ATIO
WUU
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COMPONENT SELECTION
Table 1. Inductor Vendor Information
SUPPLIER PHONE FAX WEB SITE
Coilcraft [phone] [phone] www.coilcraft.com
CoEv Magnetics [phone] [phone] www.circuitprotection.com/magnetics.asp
Murata [phone] [phone] www.murata.com
[phone]
Sumida USA: [phone] USA: [phone] www.sumida.com
Japan: 81(3) 3607-5111 Japan: 81(3) 3607-5144
TDK [phone] [phone] www.component.tdk.com
TOKO [phone] [phone] www.tokoam.com
Figure 6. Recommended Component Placement. Traces Carrying
High Current Should be Short and Wide. Trace Area at FB and V
C
Pins are Kept Low. Lead Length to Battery Should be Kept Short.
V
OUT
and V
IN
Ceramic Capacitors Close to the IC Pins.
Inductor Selection
The high frequency operation of the LTC3442 allows the
use of small surface mount inductors. The inductor ripple
current is typically set to 20% to 40% of the maximum
inductor current. For a given ripple the inductance terms
are given as follows:
L
VVV
fIV
H
L
BOOST
IN MIN OUT IN MIN
L OUT
>
∆
() ()
•( – )
••
BBUCK
OUT IN MAX OUT
LINMAX
VV V
fIV
H>
∆
•( – )
••
()
()
12
11
10
9
8
7
1
2
3
4
5
6
FB
V
C
R
LIM
V
IN
V
OUT
BURST
SHDN/SS
RT
SGND
SW1
PGND
SW2
V
IN
V
OUT
GND
R
T
MULTIPLE
VIAS
3442 F06
V
IN
where f = operating frequency, Hz
∆I
L
= maximum allowable inductor ripple current, A
V
IN(MIN)
= minimum input voltage, V
V
IN(MAX)
= maximum input voltage, V
V
OUT
= output voltage, V
I
OUT(MAX)
= maximum output load current
For high efficiency, choose a ferrite inductor with a high
frequency core material to reduce core loses. The inductor
should have low ESR (equivalent series resistance) to
reduce the I
2
R losses, and must be able to handle the peak
inductor current without saturating. Molded chokes or
chip inductors usually do not have enough core to support
the peak inductor currents in the 1A to 2A region. To
minimize radiated noise, use a shielded inductor. See
Table 1 for a suggested list of inductor suppliers.
Output Capacitor Selection
The bulk value of the output filter capacitor is set to reduce
the ripple due to charge into the capacitor each cycle. The
steady state ripple due to charge is given by:
% RIPPLE_BOOST =
IVV
CV f
OUT MAX OUT IN MIN
OUT OUT
() ()
•( – )•
••
%
100
2
% RIPPLE_BUCK =
IVV
CV Vf
OUT MAX IN MAX OUT
OUT IN MAX OUT
() ()
()
•( – )•
•••
%
100
where C
OUT
= output filter capacitor in Farads and
f = switching frequency in Hz.