LTC3554 Datasheet, PDF (24/36 Pages) Linear Technology – Micropower USB Power Manager with Li-Ion Charger and Two Step-Down Regulators

LTC3554
OPERATION
Inductor value should be chosen based on the desired
output voltage. See Table 2. 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.
Larger value inductors reduce ripple current, which
improves output ripple voltage. Lower value inductors
result in higher ripple current and improved transient
response time, but will reduce the available output cur-
rent. To maximize efficiency, choose an inductor with a
low DC resistance.
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 induc-
tor should be rated to handle the maximum peak current
specified 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
Table 1. 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 2. Choosing the Inductor Value
DESIRED OUTPUT VOLTAGE RECOMMENDED INDUCTOR VALUE
1.8V or Less
10μH
1.8V to 2.5V
6.8μH
2.5V to 3.3V
4.7μH
Table 3. Recommended Inductors for Step-Down Switching Regulators
INDUCTOR PART NO.
1117AS-4R7M
1117AS-6R8M
1117AS-100M
L (μH)
4.7
6.8
10
MAX I_DC (A)
0.64
0.54
0.45
MAX DCR (Ω)
0.18*
0.250*
0.380*
CDRH2D11BNP-4R7N
4.7
CDRH2D11BNP-6R8N
6.8
CDRH2D11BNP-100N
10
0.7
0.248
0.6
0.284
0.48
0.428
SD3112-4R7-R
SD3112-6R8-R
SD3112-100-R
4.7
0.8
0.246*
6.8
0.68
0.291*
10
0.55
0.446*
EPL2014-472ML_
EPL2014-682ML_
EPL2014-103ML_
4.7
0.88
0.254
6.8
0.8
0.316
10
0.6
0.416
* = Typical DCR
SIZE (L × W × H) (mm) MANUFACTURER
3.0 × 2.8 × 1.0
Toko
www.toko.com
3.0 × 3.0 × 1.2
Sumida
www.sumida.com
3.1 × 3.1 × 1.2
Cooper
www.cooperet.com
2.0 × 1.8 × 1.4
Coilcraft
www.coilcraft.com
3554p
24