LTC3577-3 Datasheet, PDF (33/52 Pages) Linear Technology – Highly Integrated Portable Product PMIC

LTC3577-3/LTC3577-4
OPERATION
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 step-down converters. Different
core materials and shapes will change the size/current
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 versus size, performance, and any radiated
EMI requirements than on what the step-down switching
regulators requires to operate. The inductor value also has
an effect on Burst Mode operation. Lower inductor values
will cause Burst Mode switching frequency to increase.
Table 3 shows several inductors that work well with the
step-down switching regulators. These inductors offer 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 both step-down switching regulator
outputs as well as at each step-down switching regulator
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 sufficient for the step-down
switching regulator outputs. For good transient response
and stability the output capacitor for step-down switching
regulators should retain at least 4μF of capacitance over
operating temperature and bias voltage. Each switching
regulator input supply should be bypassed with a 2.2μF
capacitor. Consult with capacitor manufacturers for de-
tailed information on their selection and specifications
of ceramic capacitors. Many manufacturers now offer
Table 3. Recommended Inductors for Step-Down Switching Regulators
INDUCTOR TYPE
DB318C
D312C
DE2812C
L (μH)
4.7
3.3
4.7
3.3
4.7
3.3
MAX I_DC (A)
1.07
1.20
0.79
0.90
1.15
1.37
MAX DCR (Ω)
0.1
0.07
0.24
0.20
0.13*
0.105*
SIZE in mm (L × W × H)
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
CDRH3D16
CDRH2D11
CLS4D09
4.7
0.9
3.3
1.1
4.7
0.5
3.3
0.6
4.7
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
SD3118
SD3112
SD12
SD10
4.7
1.3
3.3
1.59
4.7
0.8
3.3
0.97
4.7
1.29
3.3
1.42
4.7
1.08
3.3
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
LPS3015
4.7
1.1
0.2
3.3
1.3
0.13
3.0 × 3.0 × 1.5
3.0 × 3.0 × 1.5
*Typical DCR
MANUFACTURER
Toko
www.toko.com
Sumida
www.sumida.com
Cooper
www.cooperet.com
Coil Craft
www.coilcraft.com
357734fa
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