LTC3576-1_15 Datasheet, PDF (35/48 Pages) Linear Technology – Switching Power Manager with USB On-the-Go Triple Step-Down DC/DCs

LTC3576/LTC3576-1
APPLICATIONS INFORMATION
The inductor value also has an effect on Burst Mode op-
eration. Lower inductor values will cause the Burst Mode
operation switching frequency to increase.
Table 8 shows several inductors that work well with the
LTC3576/LTC3576-1’s general purpose 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.
Table 8. Recommended Inductors
MAX MAX
INDUCTOR L I_DC DCR
TYPE
(μH) (A) (Ω)
SIZE IN mm
(L × W × H) MANUFACTURER
DE2818C
D312C
DE2812C
4.7 1.25 0.072 3.0 × 2.8 × 1.8 Toko
3.3 1.45 0.053 3.0 × 2.8 × 1.8 www.toko.comm
4.7 0.79 0.24 3.6 × 3.6 × 1.2
3.3 0.90 0.20 3.6 × 3.6 × 1.2
2.2 1.14 0.14 3.6 × 3.6 × 1.2
4.7 1.2 1.13* 3.0 × 2.8 × 1.2
3.3 1.4 0.10* 3.0 × 2.8 × 1.2
2.0 1.8 0.067* 3.0 × 2.8 × 1.2
CDRH3D16 4.7 0.9 0.11 4.0 × 4.0 × 1.8 Sumida
3.3 1.1 0.085 4.0 × 4.0 × 1.8 www.sumida.com
2.2 1.2 0.072 4.0 × 4.0 × 1.8
CDRH2D11 4.7 0.5 0.17 3.2 × 3.2 × 1.2
3.3 0.6 0.123 3.2 × 3.2 × 1.2
2.2 0.78 0.098 3.2 × 3.2 × 1.2
CLS4D09 4.7 0.75 0.19 4.9 × 4.9 × 1.0
SD3118
SD3112
SD12
SD10
4.7 1.3 0.162 3.1 × 3.1 × 1.8 Cooper
3.3 1.59 0.113 3.1 × 3.1 × 1.8 www.cooperet.com
2.2 2.0 0.074 3.1 × 3.1 × 1.8
4.7 0.8 0.246 3.1 × 3.1 × 1.2
3.3 0.97 0.165 3.1 × 3.1 × 1.2
2.2 1.12 0.14 3.1 × 3.1 × 1.2
4.7 1.29 0.117* 5.2 × 5.2 × 1.2
3.3 1.42 0.104* 5.2 × 5.2 × 1.2
2.2 1.80 0.075* 5.2 × 5.2 × 1.2
4.7 1.08 0.153* 5.2 × 5.2 × 1.0
3.3 1.31 0.108* 5.2 × 5.2 × 1.0
2.2 1.65 0.091* 5.2 × 5.2 × 1.0
LPS3015
4.7 1.1 0.2 3.0 × 3.0 × 1.5 Coilcraft
3.3 1.3 0.13 3.0 × 3.0 × 1.5 www.coilcraft.com
2.2 1.5 0.11 3.0 × 3.0 × 1.5
*Typical DCR
Step-Down Switching Regulator Input/Output Bypass
Capacitor Selection
Low ESR (equivalent series resistance) MLCCs should
be used at each switching regulator output as well as at
each switching regulator input supply (V_INx). 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 capaci-
tor is sufficient for most applications. For good transient
response and stability the output capacitor should retain
at least 4μF of capacitance over operating temperature and
bias voltage. Each switching regulator input supply should
be bypassed with a 1μF capacitor. Consult with capacitor
manufacturers for detailed information on their selection
and specifications of ceramic capacitors. Many manufac-
turers now offer very thin (<1mm tall) ceramic capacitors
ideal for use in height-restricted designs. Table 9 shows a
list of several ceramic capacitor manufacturers.
Table 9. Recommended 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
Overvoltage Protection
V_BUS can be protected from overvoltage damage with two
additional components, a resistor R1 and an N-channel
MOSFET MN1, as shown in Figure 6. Suitable choices for
MN1 are listed in Table 10.
Table 10. Recommended N-channel MOSFETs for the
Overvoltage Protection Circuit
PART NUMBER
Si1472DH
BVDSS
30V
R_ON
82mΩ
PACKAGE
SC70-6
Si2302ADS
20V
60mΩ
SOT-23
Si2306BDS
30V
65mΩ
SOT-23
Si2316BDS
30V
80mΩ
SOT-23
IRLML2502
20V
35mΩ
SOT-23
FDN372S
30V
50mΩ
SOT-23
NTLJS4114N
30V
35mΩ
WDFN6
R1 is a 6.2k resistor and must be rated for the power dis-
sipated during maximum overvoltage. In an overvoltage
condition the OVSENS pin will be clamped at 6V. R1 must
be sized appropriately to dissipate the resultant power.
For example, a 1/10W 6.2k resistor can have at most
√P_MAX • 6.2kΩ = 25V applied across its terminals. With
the 6V at OVSENS, the maximum overvoltage magnitude
that this resistor can withstand is 31V. A 1/4W 6.2k resistor
raises this value to 45V. OVSENS’s absolute maximum
current rating of 10mA imposes an upper limit of 68V
protection.
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