LT3472 データシートの表示（PDF） - Linear Technology
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LT3472 Datasheet PDF : 12 Pages
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LT3472
APPLICATIO S I FOR ATIO
Table 1. Recommended Inductors
Part No.
Inductance DCR Current Manufacturer
(µH) (Ω) Rating (mA)
LQH32CN220
LQH32CN470
LQH2MCN220
LQH2MCN470
22
0.71
250
Murata
47
1.3
170 (814) 237-1431
22
2.1
185 www.murata.com
47
5.1
120
D1067FB-220M
22
2.0
270 TOKO
(408) 432-8281
www.tokoam.com
ELJPC220KF
22
4.0
160 Panasonic
(714) 373-7334
www.panasonic.com
CDRH3D16-220
22
0.53
350 Sumida
(847) 956-0666
www.sumida.com
LB2012B220M
22
1.7
75
Taiyo Yuden
LEM2520-220
22
5.5
125 (408) 573-4150
www.t-yuden.com
Capacitor Selection
The small size of ceramic capacitors makes them suitable
for LT3472 applications. X5R and X57 types of ceramic
capacitors are recommended because they retain their
capacitance over wider voltage and temperature ranges
than other types such as Y5V or Z5U. A 2.2µF input
capacitor and a 2.2µF output capacitor are sufficient for
most LT3472 applications.
Table 2. Recommended Ceramic Capacitor Manufacturers
Manufacturer
Phone
URL
Taiyo Yuden
(408) 573-4150
www.t-yuden.com
Murata
(814) 237-1431
www.murata.com
Kemet
(408) 986-0424
www.kemet.com
Inrush Current
The LT3472 uses internal Schottky diodes. When supply
voltage is abruptly applied to VIN pin, for the positive
channel, the voltage difference between VIN and VPOS
generates inrush current flowing from input through the
inductor LP and the internal Schottky diode DP to charge
the output capacitor COP. For the inverter channel, there is
a similar inrush current flowing from input through the
inductor LN1 path, charging the capacitor CNF, and return-
ing through the internal Schottky diode DN. The maximum
current the Schottky diodes in the LT3472 can sustain is
1A. The selection of inductor and capacitor value should
ensure the peak of the inrush current to be below 1A. The
peak inrush current can be calculated as follows:
IP
=
VIN – 0.6
L•ω
• EXP⎡⎣⎢–
α
ω
•
arctan
⎛
⎝⎜
ω⎞⎤
α ⎠⎟ ⎦⎥
•
SIN⎡⎣⎢arctan•
⎛⎝⎜
ω
α
⎞⎠⎟
⎤
⎦⎥
α
=
r + 1.5
2•L
ω=
1
L•C
–
4
r
• L2
where L is the inductance, r is the resistance of the
inductor and C is the output capacitance. For low DCR
inductors, which is usually the case for this application,
the peak inrush current can be simplified as follows:
IP
=
VIN
L
– 0.6
•ω
⎛
• EXP⎝⎜
–
α
ω
•
π⎞
2 ⎠⎟
Table 3 gives inrush peak currents for some component
selections. Note that inrush current is not a concern if the
input voltage rises slowly.
Table 3. Inrush Peak Current
VIN (V)
r (Ω)
L (µH)
C (µF)
IP (A)
5
0.5
22
2.2
0.89
3.6
0.7
22
2.2
0.59
3.6
2.1
22
2.2
0.46
3.6
1.3
47
1
0.32
3.6
0.7
22
1
0.46
External Diode Selection
As stated previously the LT3472 has internal Schottky
diodes. The Schottky diode DP is sufficient for most step-
up applications. However, for high current inverter appli-
cations, a properly selected external Schottky diode in
parallel with DN can improve efficiency. For external diode
selection, both forward voltage drop and diode capaci-
tance need to be considered. Schottky diodes rated for
higher current usually have lower forward voltage drop
3472f
7
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