LTC3566-2_15 Datasheet, PDF (20/28 Pages) Linear Technology – High Efficiency USB Power Manager Plus 1A Buck-Boost Converter

LTC3566/LTC3566-2
APPLICATIONS INFORMATION
Buck-Boost Regulator Inductor Selection
Many different sizes and shapes of inductors are avail-
able from numerous manufacturers. Choosing the right
inductor from such a large selection of devices can be
overwhelming, but following a few basic guidelines will
make the selection process much simpler.
The buck-boost converter is designed to work with induc-
tors in the range of 1μH to 5μH. For most applications a
2.2μH inductor will suffice. Larger value inductors reduce
ripple current which improves output ripple voltage. Lower
value inductors result in higher ripple current and improved
transient response time. To maximize efficiency, choose
an inductor with a low DC resistance. For a 3.3V output,
efficiency is reduced about 3% for a 100mΩ series resis-
tance at 1A load current, and about 2% for 300mΩ series
resistance at 200mA load current. 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 2.5A maximum peak current specified for the
buck-boost converter.
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 do not 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 LTC3566 family requires
to operate.
The inductor value also has an effect on Burst Mode op-
eration. Lower inductor values will cause the Burst Mode
operation switching frequencies to increase.
Table 5 shows several inductors that work well with the
LTC3566 family’s buck-boost regulator. 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-Boost Regulator
INDUCTOR TYPE
LPS4018
L (μH)
3.3
2.2
MAX I_DC (A)
2.2
2.5
MAX DCR (Ω)
0.08
0.07
D53LC
2.0
3.25
0.02
7440430022
2.2
2.5
0.028
CDRH4D22/HP
2.2
2.4
0.044
SD14
2.0
2.56
0.045
SIZE IN mm (L × W × H)
3.9 × 3.9 × 1.7
3.9 × 3.9 × 1.7
5.0 × 5.0 × 3.0
4.8 × 4.8 × 2.8
4.7 × 4.7 × 2.4
5.2 × 5.2 × 1.45
MANUFACTURER
Coilcraft
www.coilcraft.com
Toko
www.toko.com
Würth Elektronik
www.we-online.com
Sumida
www.sumida.com
Cooper
www.cooperet.com
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