LTC3535_15 Datasheet, PDF (12/16 Pages) Linear Technology – Dual Channel 550mA 1MHz Synchronous Step-Up DC/DC Converter

LTC3535
APPLICATIONS INFORMATION
COMPONENT SELECTION
Inductor Selection
The LTC3535 can utilize small surface mount chip induc-
tors due to their fast 1MHz switching frequency. Inductor
values between 3.3µH and 6.8µH are suitable for most
applications. Larger values of inductance will allow slightly
greater output current capability (and lower the Burst
Mode threshold) by reducing the inductor ripple current.
Increasing the inductance above 10µH will increase com-
ponent size while providing little improvement in output
current capability.
The minimum inductance value is given by:
( ) L > VIN(MIN) • VOUT(MAX) – VIN(MIN)
Ripple • V_OUT(MAX)
where:
Ripple = Allowable inductor current ripple (amps peak-
peak)
V_IN(MIN) = Minimum input voltage
V_OUT(MAX) = Maximum output voltage
The inductor current ripple is typically set for 20% to
40% of the maximum inductor current. High frequency
ferrite core inductor materials reduce frequency dependent
power losses compared to cheaper powdered iron types,
improving efficiency. The inductor should have low ESR
(series resistance of the windings) to reduce the I²R power
losses, and must be able to support the peak inductor
current without saturating. Molded chokes and some chip
inductors usually do not have enough core area to support
the peak inductor current of 750mA seen on the LTC3535.
To minimize radiated noise, use a shielded inductor. See
Table 1 for suggested components and suppliers.
Table 1. Recommended Inductors
VENDOR
PART/STYLE
Coilcraft
[phone]
www.coilcraft.com
LPO4815
LPS4012, LPS4018
MSS5131
MSS4020
MOS6020
ME3220
DS1605, DO1608
Coiltronics
www.cooperet.com
SD10, SD12, SD14, SD18, SD20,
SD52, SD3114, SD3118
FDK
[phone]
www.fdk.com
MIP3226D4R7M, MIP3226D3R3M
MIPF2520D4R7
MIPWT3226D3R0
Murata
[phone]
www.murata.com
LQH43C
LQH32C (-53 series)
301015
Sumida
[phone]
www.sumida.com
CDRH5D18
CDRH2D14
CDRH3D16
CDRH3D11
CR43
CMD4D06-4R7MC
CMD4D06-3R3MC
Taiyo-Yuden
www.t-yuden.com
NP03SB
NR3015T
NR3012T
TDK
[phone]
www.component.tdk.com
VLP
VLF, VLCF
Toko
[phone]
www.tokoam.com
D412C
D518LC
D52LC
D62LCB
Wurth
[phone]
www.we-online.com
WE-TPC type S, M
Output and Input Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used to minimize the output voltage ripple. Multilayer
ceramic capacitors are an excellent choice as they have
extremely low ESR and are available in small footprints. A
3535fa
12