LT3472

7

3472f

Table 1. Recommended Inductors

Part No.

Inductance DCR

Current

Manufacturer

(µH)

(Ω) Rating (mA)

LQH32CN220

22

0.71

250

Murata

LQH32CN470

47

1.3

170

(814) 237-1431

LQH2MCN220

22

2.1

185

www.murata.com

LQH2MCN470

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

generates inrush current flowing from input through the

a similar inrush current flowing from input through the

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:

I

V

L

EXP

SIN

r

L

LC

r

L

P

IN

=

⎛

⎝

⎜

⎞

⎠

⎟

⎡

⎣

⎢

⎤

⎦

⎥

⎛

⎝

⎜

⎞

⎠

⎟

⎡

⎣

⎢

⎤

⎦

⎥

=

+

=

–.

•

•

–

• arctan

•

arctan•

.

•

•

–

•

06

15

2

1

4

2

ω

α

ω

ω

α

ω

α

α

ω

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:

I

V

L

EXP

P

IN

=

⎛

⎝

⎜

⎞

⎠

⎟

–.

•

•–

•

06

2

ω

α

ω

π

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

r (Ω)L (µH)

C (µF)

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

up applications. However, for high current inverter appli-

cations, a properly selected external Schottky diode in

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

APPLICATIO S I FOR ATIO