LTC3452 Linear Technology, LTC3452 Datasheet - Page 11

• Manufacturer Part Number: LTC3452
• Description: Synchronous Buck-Boost MAIN/CAMERA White LED Driver
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
COMPONENT SELECTION
Inductor Selection
The high frequency operation of the LTC3452 allows the
use of small surface mount inductors. The inductor cur-
rent ripple is typically set to 20% to 40% of the maximum
average inductor current. For a given ripple the inductance
term in boost mode is:
and in buck mode is:
where:
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 peak inductor currents >1A. To minimize radi-
ated noise, use a toroid, pot core or shielded bobbin
inductor. For the white LED application, a 4.7µH inductor
value is recommended. See Table 2 for a list of component
suppliers.
Table 2. Inductor Vendor Information
SUPPLIER
Coilcraft
Cooper/Coiltronics
Murata
Sumida
Vishay-Dale
f = operating frequency, Hz
%Ripple = allowable inductor current ripple, %
V
V
V
I
L
L
OUT(MAX)
IN(MIN)
IN(MAX)
OUT
>
>
V
f I
V
IN MIN
•
OUT
= output voltage, V
f I
(
OUT MAX
•
= minimum input voltage, V
= maximum input voltage, V
OUT MAX
•
= maximum output load current
(
)
(
2
V
(
IN MAX
•
(
(
)
V
U
• %
OUT
)
• • %
)
Rip
–
–
U
Ripple V
V
V
2
p p le V
OUT
R losses, and must be able to
IN MIN
(
WEB SITE
www.coilcraft.com
www.cooperet.com
www.murata.com
www.japanlink.com/sumida
www.vishay.com
•
)
•
IN MAX
•
)
100
)
(
W
OUT
•
100
%
2
)
%
U
Input Capacitor Selection
Since the V
recommended to place at least a 2.2µF, low ESR bypass
capacitor to ground. See Table 3 for a list of component
suppliers.
Table 3. Capacitor Vendor Information
SUPPLIER
AVX
Sanyo
Taiyo Yuden
TDK
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
above calculations in order to maintain the desired tran-
sient response.
The other component of ripple is due to the ESR (equiva-
lent series resistance) of the output capacitor. Low ESR
capacitors should be used to minimize output voltage
ripple. For surface mount applications, Taiyo Yuden, TDK,
AVX ceramic capacitors, AVX TPS series tantalum capaci-
tors or Sanyo POSCAP are recommended. For the white
LED application, a 4.7µF capacitor value is recommended.
See Table 3 for a list of component suppliers.
%
%
Ripple Boost
Ripple Buck
OUT
_
_
IN
= output filter capacitor, F
pin is the supply voltage for the IC it is
=
=
8
I
(
OUT MAX
•
V
IN MAX
V
IN MAX
(
(
(
)
)
C C
WEB SITE
www.avxcorp.com
www.sanyovideo.com
www.t-yuden.com
www.component.tdk.com
)
•
–
OUT
•
(
V
V
f
OUT
www.DataSheet4U.com
2
OUT
•
• •
V
L C
)
OUT
–
•
1 1 00
V
OUT
IN MIN
2
LTC3452
(
•
f
%
)
)
•
11
100
3452f
%