LTC3425 Linear Technology, LTC3425 Datasheet - Page 17

• Manufacturer Part Number: LTC3425
• Description: 5A 8MHz 4-Phase Synchronous Step-Up DC/DC Converter
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
COMPONENT SELECTION
Inductor Selection
The high frequency, multiphase operation of the LTC3425
allows the use of small surface mount inductors. The
minimum inductance value is proportional to the operat-
ing frequency and is limited by the following constraints:
where:
Figure 6. Example Board Layout for a 10W, 4-Phase Boost
Converter. Total Area = 0.50in
on the Topside of Board)
f = Operating frequency in MHz (of each phase)
Ripple = Allowable inductor current ripple (amps
peak-peak)
V
V
L
IN(MIN)
OUT(MAX)
2
f
C
C
L1
L2
OUT
OUT
and L
= Minimum input voltage
= Maximum output voltage
Figure 5. Typical Board Layout
U
C
SS
V
IN MIN
C
IN
(
U
LTC3425
f Ripple V
2
LTC3425
•
(with All Components Mounted
)
•
V
3425 F06
OUT MAX
R
W
T
•
(
OUT MAX
)
(
–
C
C
OUT
OUT
V
L4
L3
U
IN MIN
)
(
3425 F05
)
The inductor current ripple is typically set to 20% to 40%
of the maximum inductor current.
For high efficiency, choose an inductor with 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. To
minimize radiated noise, use a shielded inductor. (Note
that the inductance of shielded types will drop more as
current increases, and will saturate more easily). See
Table 2 for a list of inductor manufacturers.
Table 2. Inductor Vendor Information
SUPPLIER PHONE
Coilcraft
Murata
Sumida
TDK
Some example inductor part types are:
Output Capacitor Selection
The output voltage ripple has three components to it. The
bulk value of the capacitor is set to reduce the ripple due
to charge into the capacitor each cycle. The max ripple due
to charge is given by:
where:
Coilcraft DO-1608, DS-1608 and DT-1608 series
Murata LQH3C, LQH4C, LQH32C and LQN6C series
Sumida CDRH3D16, CDRH4D18, CDRH4D28, CR32,
CR43 series
TDK RLF5018T and NLFC453232T series
I
f = switching frequency of one phase
V
P
RBULK
= peak inductor current
[phone]
USA:
[phone]
USA:
[phone]
Japan:
81-3-3607-5111
[phone]
C
OUT
I
•
P
V
•
OUT
V
IN
FAX
[phone]
USA:
[phone]
USA:
[phone]
Japan:
81-3-3607-5144
[phone]
2
• • 4
R losses, and must be able to
f
www.DataSheet4U.com
LTC3425
WEB SITE
www.coilcraft.com
www.murata.com
www.japanlink.com/
sumida
www.component.
tdk.com
17
3425f