LTC3401 Linear Technology, LTC3401 Datasheet - Page 9

• Manufacturer Part Number: LTC3401
• Description: 1A/ 3MHz Micropower Synchronous Boost Converter
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
Burst Mode operation is user controlled by driving the
MODE/SYNC pin high to enable and low to disable. It is
recommended that Burst Mode operation be entered after
the part has started up.
COMPONENT SELECTION
Inductor Selection
The high frequency operation of the LTC3401 allows the
use of small surface mount inductors. The minimum
inductance value is proportional to the operating fre-
quency and is limited by the following constraints:
where
The inductor current ripple is typically set to 20% to 40%
of the maximum inductor current.
For high efficiency, choose an inductor with a high fre-
quency core material, such as ferrite, to reduce core
losses. The inductor should have low ESR (equivalent
series resistance) to reduce the I
able to handle the peak inductor current at full load without
saturating. Molded chokes or chip inductors usually do
not have enough core to support the peak inductor cur-
rents in the 1A to 2A region. To minimize radiated noise,
use a toroid, pot core or shielded bobbin inductor. See
Table 1 for a list of component suppliers.
Table 1. Inductor Vendor Information
SUPPLIER
Coilcraft
Coiltronics
Murata
Sumida
L
f = Operating Frequency (Hz)
Ripple = Allowable Inductor Current Ripple (A)
V
V
IN(MIN)
OUT(MAX)
3
f
Japan: 81-3-3607-5111 81-3-3607-5144
USA: [phone]
H and L
= Minimum Input Voltage (V)
PHONE
[phone]
[phone]
[phone]
[phone]
= Maximum Output Voltage (V)
U
V
IN MIN
(
f Ripple V
U
FAX
[phone]
[phone]
[phone]
[phone]
•
)
•
V
OUT MAX
2
R losses and must be
•
W
(
OUT MAX
)
WEBSITE
www.coilcraft.com
www.coiltronics.com
www.murata.com
www.japanlink.com
sumida
(
–
V
IN MIN
)
(
U
)
H
Table 2. Capacitor Vendor Information
SUPPLIER
AVX
Sanyo
Taiyo Yuden [phone]
Output Capacitor Selection
The output voltage ripple has several components. 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
The ESR can be a significant factor for ripple in most power
converters. The ripple due to capacitor ESR is simply given
by:
where
Low ESR capacitors should be used to minimize output
voltage ripple. For surface mount applications, AVX TPS
series tantalum capacitors, Sanyo POSCAP, or Taiyo-
Yuden ceramic capacitors are recommended. For through-
hole applications Sanyo OS-CON capacitors offer low ESR
in a small package size. See Table 2 for a list of component
suppliers.
Figure 1. Recommended Component Placement. Traces
Carrying High Current Are Direct. Trace Area FB and V
Are Kept Low. Lead Length to Battery Should be Kept Short
I
VR
R
VR
P
ESR
= Peak Inductor Current
CESR
BULK
= Capacitor Series Resistance
= I
PHONE
[phone]
[phone]
P
C
• R
OUT
I
ESR
P
V
•
•
OUT
V
V
V
OUT
IN
FAX
[phone]
[phone]
[phone]
R
MODE
V
SW
GND
t
IN
•
f
PGOOD
V
SHDN
V
OUT
V
FB
C
WEBSITE
www.avxcorp.com
www.sanyovideo.com
www.t-yuden.com
LTC3401
3401 F01
C
Pins
3401fa
9