LTC3586_15 Datasheet, PDF (29/36 Pages) Linear Technology – High Efficiency USB Power Manager with Boost, Buck-Boost and Dual Bucks

LTC3586/LTC3586-1
Applications Information
load current. Choose an inductor with a DC current rating
at least 1.5 times larger than the maximum load current to
ensure that the inductor does not saturate during normal
operation. If output short circuit is a possible condition,
the inductor should be rated to handle the maximum peak
current specified for the buck converters.
Different core materials and shapes will change the size/cur-
rent and price/current relationship of an inductor. Toroid
or shielded pot cores in ferrite or Permalloy materials are
small and don’t radiate much energy, but generally cost
more than powdered iron core inductors with similar
electrical characteristics. Inductors that are very thin or
have a very small volume typically have much higher
core and DCR losses, and will not give the best efficiency.
The choice of which style inductor to use often depends
more on the price vs size, performance and any radiated
EMI requirements than on what the LTC3586/LTC3586-1
require to operate.
The inductor value also has an effect on Burst Mode
operations. Lower inductor values will cause the Burst
Mode switching frequencies to increase.
Table 5 shows several inductors that work well with the
LTC3586/LTC3586-1’s buck regulators. These inductors of-
fer a good compromise in current rating, DCR and physical
size. Consult each manufacturer for detailed information
on their entire selection of inductors.
Table 5. Recommended Inductors for Buck Regulators
MAX MAX
INDUCTOR L I_DC DCR
TYPE
(µH) (A) (Ω)
SIZE IN mm
(L × W × H) MANUFACTURER
DE2818C
DE2812C
4.7 1.25 0.072* 3.0 × 2.8 × 1.8 Toko
4.7 1.15 0.13* 3.0 × 2.8 × 1.2 ^www.toko.com
CDRH3D16 4.7 0.9 0.11 4 × 4 × 1.8 Sumida
www.sumida.com
SD3118
SD3112
4.7 1.3 0.162 3.1 × 3.1 × 1.8 Cooper
4.7 0.8 0.246 3.1 × 3.1 × 1.2 ^{www.cooperet.com}
LPS3015 4.7 1.1 0.2 3.0 × 3.0 × 1.5 Coilcraft
www.coilcraft.com
*Typical DCR
Buck Regulator Input/Output Capacitor Selection
Low ESR (equivalent series resistance) MLCC capacitors
should be used at both buck regulator outputs as well as at
each buck regulator input supply (V_IN1 and V_IN2). Only X5R
or X7R ceramic capacitors should be used because they
retain their capacitance over wider voltage and temperature
ranges than other ceramic types. A 10µF output capaci-
tor is sufficient for most applications. For good transient
response and stability the output capacitor should retain
at least 4µF of capacitance over operating temperature
and bias voltage. Each buck regulator input supply should
be bypassed with a 1µF capacitor. Consult with capacitor
manufacturers for detailed information on their selection
and specifications of ceramic capacitors. Many manufac-
turers now offer very thin (<1mm tall) ceramic capacitors
ideal for use in height-restricted designs. Table 6 shows a
list of several ceramic capacitor manufacturers.
Table 6. Recommended Ceramic Capacitor Manufacturers
AVX
www/avxcorp.com
Murata
www.murata.com
Taiyo Yuden
www.t-yuden.com
Vishay Siliconix
www.vishay.com
TDK
www.tdk.com
BUCK-BOOST REGULATOR APPLICATIONS SECTION
Buck-Boost Regulator Inductor Selection
Inductor selection criteria for the buck-boost are similar
to those given for the buck switching regulator. The buck-
boost converter is designed to work with inductors in the
range of 1µH to 5µH. For most applications a 2.2µH inductor
will suffice. Choose an inductor with a DC current rating
at least 2 times larger than the maximum load current to
ensure that the inductor does not saturate during normal
operation. If output short circuit is a possible condition,
the inductor should be rated to handle the maximum peak
current specified for the buck-boost converter.
Table 7 shows several inductors that work well with the
LTC3586/LTC3586-1’s buck-boost regulator. These induc-
tors offer a good compromise in current rating, DCR and
physical size. Consult each manufacturer for detailed
information on their entire selection of inductors.
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