LTC3443 Linear Technology, LTC3443 Datasheet - Page 11

• Manufacturer Part Number: LTC3443
• Description: High Current Micropower 600kHz Synchronous Buck-Boost DC/DC Converter
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
Figure 6. Recommended Component Placement. Traces Carrying
High Current are Direct. Trace Area at FB and V
Low. Lead Length to Battery Should be Kept Short. V
Ceramic Capacitors Close to the IC Pins
COMPONENT SELECTION
Inductor Selection
The high frequency operation of the LTC3443 allows the
use of small surface mount inductors. The inductor cur-
rent ripple is typically set to 20% to 40% of the maximum
inductor current. For a given ripple the inductance terms
are given as follows:
where f = operating frequency, Hz
%Ripple = allowable inductor current ripple, %
V
V
V
I
OUT(MAX)
IN(MIN)
IN(MAX)
OUT
L
L
>
>
= output voltage, V
V
f I
IN MIN
f I
V
•
= minimum input voltage, V
= maximum input voltage, V
•
OUT
= maximum output load current
(
OUT MAX
OUT MAX
(
)
•
2
(
(
V
•
1
2
3
4
5
6
IN MAX
(
)
V
U
SHDN/SS
GND
PGND
SW1
SW2
PGND
(
)
• %
OUT
• %
Ripple V
)
–
Ripple V
U
–
GND
V
V
IN MIN
OUT
MODE
(
V
PV
OUT
•
V
FB
V
IN
IN
•
C
)
IN MAX
)
12
11
10
MULTIPLE VIAS
•
9
8
7
W
)
OUT
(
100
•
100
2
)
C
H
H
Pins are Kept
,
V
V
IN
OUT
OUT
U
3443 F06
and V
IN
For high efficiency, choose an inductor with a high fre-
quency core material, such as ferrite, to reduce core loses.
The inductor should have low ESR (equivalent series
resistance) to reduce the I
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 toroid, pot core
or shielded bobbin inductor. See Table 1 for suggested
components and Table 2 for a list of component suppliers.
Table 1. Inductor Vendor Information
SUPPLIER
Coilcraft
Coiltronics
Murata
Sumida
Output Capacitor Selection
The bulk value of the 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:
where C
The output capacitance is usually many times larger in
order to handle the transient response of the converter.
For a rule of thumb, the ratio of the operating frequency to
the unity-gain bandwidth of the converter is the amount
the output capacitance will have to increase from the
%
%
Ripple Boost
Ripple Buck
OUT
_
_
PHONE
[phone]
[phone]
USA:
[phone]
[phone]
USA:
[phone]
Japan:
81(3) 3607-5111 81(3) 3607-5144
= output filter capacitor, F
=
=
I
OUT MAX
I
OUT MAX
(
(
C
FAX
[phone]
[phone]
USA:
[phone]
[phone]
OUT
2
R losses, and must be able to
)
)
C
•
•
•
OUT
(
V
(
V
IN MAX
V
IN MAX
www.DataSheet4U.com
OUT
(
(
•
V
OUT
–
)
)
LTC3443
WEB SITE
www.coilcraft.com
www.coiltronics.com
www.murata.com
www.japanlink.com/
sumida
V
•
–
IN MIN
2
V
V
(
OUT
•
OUT
f
)
•
)
)
sn3443 3443fs
f
•
•
11
100
100
%
%