LTC3557_15 Datasheet, PDF (20/28 Pages) Linear Technology – USB Power Manager with Li-Ion Charger and Three Step-Down Regulators

LTC3557/LTC3557-1
OPERATION
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.
Step-Down Switching Regulator 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
detailed information on their selection and specifications
of ceramic capacitors. Many manufacturers now offer
very thin (<1mm tall) ceramic capacitors ideal for use in
height-restricted designs. Table 4 shows a list of several
ceramic capacitor manufacturers.
Table 4. 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
Table 3. Recommended Inductors for Step-Down Switching Regulators
INDUCTOR TYPE
DE2818C
D312C
DE2812C
CDRH3D16
CDRH2D11
CLS4D09
SD3118
SD3112
SD12
SD10
LPS3015
*Typical DCR
L (μH)
4.7
3.3
4.7
3.3
4.7
3.3
4.7
3.3
4.7
3.3
4.7
4.7
3.3
4.7
3.3
4.7
3.3
4.7
3.3
4.7
3.3
MAX I_DC (A)
1.25
1.45
0.79
0.90
1.2
1.4
0.9
1.1
0.5
0.6
0.75
1.3
1.59
0.8
0.97
1.29
1.42
1.08
1.31
1.1
1.3
MAX DCR (Ω)
0.072
0.053
0.24
0.20
0.13*
0.105*
0.11
0.085
0.17
0.123
0.19
0.162
0.113
0.246
0.165
0.117*
0.104*
0.153*
0.108*
0.2
0.13
SIZE in mm
(L × W × H)
3.0 × 2.8 × 1.8
3.0 × 2.8 × 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
4.0 × 4.0 × 1.8
4.0 × 4.0 × 1.8
3.2 × 3.2 × 1.2
3.2 × 3.2 × 1.2
4.9 × 4.9 × 1.0
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
3.0 × 3.0 × 1.5
3.0 × 3.0 × 1.5
MANUFACTURER
Toko
www.toko.com
Sumida
www.sumida.com
Cooper
www.cooperet.com
Coil Craft
www.coilcraft.com
35571fc
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