LTC3401
W U U
APPLICATIO S I FOR ATIO
U
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.
R
SHDN
t
MODE
V
C
V
SW
FB
OUT
IN
V
GND PGOOD
COMPONENT SELECTION
Inductor Selection
V
OUT
3401 F01
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:
Figure 1. Recommended Component Placement. Traces
Carrying High Current Are Direct. Trace Area FB and VC Pins
Are Kept Low. Lead Length to Battery Should be Kept Short
Output Capacitor Selection
V
IN(MIN) • VOUT(MAX) – V
(
IN(MIN)
)
3
L > μH and L >
H
The output voltage ripple has several components. The
bulk value of the capacitor is set to reduce the ripple due
tochargeintothecapacitoreachcycle. Themaxrippledue
to charge is given by:
f
f •Ripple • VOUT(MAX)
where
f = Operating Frequency (Hz)
Ripple = Allowable Inductor Current Ripple (A)
VIN(MIN) = Minimum Input Voltage (V)
VOUT(MAX) = Maximum Output Voltage (V)
IP • V
IN
VRBULK
=
V
COUT • VOUT • f
where
The inductor current ripple is typically set to 20% to 40%
of the maximum inductor current.
IP = Peak Inductor Current
TheESRcanbeasignificantfactorforrippleinmostpower
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 I2R losses and must be
abletohandlethepeakinductorcurrentatfullloadwithout
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.
converters.TherippleduetocapacitorESRissimplygiven
by:
VRCESR = IP • RESR
where
V
RESR = Capacitor Series Resistance
Low ESR capacitors should be used to minimize output
voltage ripple. For surface mount applications, AVX TPS
series tantalum capacitors, Sanyo POSCAP, or Taiyo-
Yudenceramiccapacitorsarerecommended.Forthrough-
hole applications Sanyo OS-CON capacitors offer low ESR
in a small package size. See Table 2 for a list of component
suppliers.
Table 1. Inductor Vendor Information
SUPPLIER
Coilcraft
PHONE
FAX
WEBSITE
(847) 639-6400 (847) 639-1469 www.coilcraft.com
(516) 241-7876 (516) 241-9339 www.coiltronics.com
Coiltronics
Murata
Table 2. Capacitor Vendor Information
(814) 237-1431 (814) 238-0490 www.murata.com
(800) 831-9172
SUPPLIER
AVX
PHONE
FAX
WEBSITE
(803) 448-9411 (803) 448-1943 www.avxcorp.com
(619) 661-6322 (619) 661-1055 www.sanyovideo.com
Sumida
Sanyo
USA: (847) 956-0666 (847) 956-0702 www.japanlink.com
Japan: 81-3-3607-5111 81-3-3607-5144 sumida
Taiyo Yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com
3401fb
9
Linear [ Linear ]
