LTC3562
16
3562fa
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 step-down converters are designed to work with induc-
tors in the range of 2.2μH to 10μH. For most applications a
4.7μH inductor is suggested for the lower power switching
regulators R400A and R400B and 3.3μH is recommended
for the more powerful switching regulators R600A and
R600B. Larger value inductors reduce ripple current which
improves output ripple voltage. Lower value inductors
result in higher ripple current and improved transient re-
sponse time, but will reduce the available output current.
To maximize effi ciency, choose an inductor with a low DC
resistance. For a 1.2V output, effi ciency is reduced about
2% for 100mΩ series resist-ance at 400mA load current,
and about 2% for 300mΩ series resistance at 100mA 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 specifi ed for the step-down 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 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 effi ciency. The
choice of which style inductor to use often depends more
on the price versus size, performance, and any radiated
EMI requirements than on what the LTC3562 requires to
operate.
The inductor value also has an effect on Burst Mode and
forced Burst Mode operations. Lower inductor values will
cause the Burst Mode and forced Burst Mode switching
frequencies to increase.
APPLICATIONS INFORMATION
Table 7 shows several inductors that work well with the
LTC3562’s general purpose 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.
Input/Output Capacitor Selection
Low ESR (equivalent series resistance) ceramic capacitors
should be used at the switching regulator outputs as well
as the input supply. 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 capacitor is suffi cient for
most applications. For good transient response and sta-
bility the output capacitor should retain at least 4μF of
capacitance over operating temperature and bias voltage.
The input supply should be bypassed with a 10μF capaci-
tor, or greater. Consult with capacitor manufacturers for
detailed information on their selection and specifi cations
of ceramic capacitors. Many manufacturers now offer
Table 7. Recommended Inductors
INDUCTOR
TYPE
L
(μH)
MAX
I
DC
(A)
MAX
DCR
(Ω)
SIZE
(mm)
(L × W × H) MANUFACTURER
DB318C
D312C
DE2812C
DE2818C
4.7
3.3
4.7
3.3
4.7
3.3
4.7
3.3
1.07
1.20
0.79
0.90
1.15
1.37
1.25
1.45
0.1
0.07
0.24
0.20
0.13*
0.105*
0.072*
0.052*
3.8 × 3.8 × 1.8
3.8 × 3.8 × 1.8
3.6 × 3.6 × 1.2
3.6 × 3.6 × 1.2
3.0 × 2.8 × 1.2
3.0 × 2.8 × 1.2
3.0 × 2.8 × 1.8
3.0 × 2.8 × 1.8
Toko
www.toko.com
CDRH3D16
CDRH2D11
CLS4D09
4.7
3.3
4.7
3.3
4.7
0.9
1.1
0.5
0.6
0.75
0.11
0.085
0.17
0.123
0.19
4 × 4 × 1.8
4 × 4 × 1.8
3.2 × 3.2 × 1.2
3.2 × 3.2 × 1.2
4.9 × 4.9 × 1
Sumida
www.sumida.com
SD3118
SD3112
SD12
SD10
4.7
3.3
4.7
3.3
4.7
3.3
4.7
3.3
1.3
1.59
0.8
0.97
1.29
1.42
1.08
1.31
0.162
0.113
0.246
0.165
0.117*
0.104*
0.153*
0.108*
3.1 × 3.1 × 1.8
3.1 × 3.1 × 1.8
3.1 × 3.1 × 1.2
3.1 × 3.1
× 1.2
5.2 × 5.2 × 1.2
5.2 × 5.2 × 1.2
5.2 × 5.2 × 1.0
5.2 × 5.2 × 1.0
Cooper
www.cooperet.com
LPS3015 4.7
3.3
1.1
1.3
0.2
0.13
3.0 × 3.0 × 1.5
3.0 × 3.0 × 1.5
Coil Craft
www.coilcraft.com
* Typical DCR
