LT3462/LT3462A

3462af

5

R2

R1

GND

C3

L1

L2

C1

C4

C2

3462 F03

1

2

34

5

6

Inrush Current

The LT3462 has a built-in Schottky diode. When supply

input through the inductor and the Schottky diode to

nonrepetitive surge current the Schottky diode in the

LT3462 can sustain is 1.5A. The selection of inductor and

capacitor value should ensure the peak of the inrush

current to be below 1.5A. The peak inrush current can be

calculated as follows:

I

VO

L

C

L

C

P

IN

=

























–.

–

exp –

–

6

12

1

π

where L is the inductance between supply and SW, and C

is the capacitance between SW and D.

Table 3 gives inrush peak currents for some component

selections.

Table 3. Inrush Peak Current

L (

µH)

C (

µF)

5

22

1

0.70

5

33

1

0.60

12

47

1

1.40

Inductor Selection

Each of the two inductors used with LT3462 should have

a saturation current rating (where inductance is approxi-

mately 70% of zero current inductance ) of approximately

0.25A or greater. If the device is used in the charge pump

mode, where there is only one inductor, then its rating

should be 0.35A or greater. DCR of the inductors should

be less than 1

Ω. For LT3462, a value of 22µH is suitable

if using a coupled inductor such as Sumida CLS62-220. If

using two separate inductors, increasing the value to

47

µH will result in the same ripple current. For LT3462A,

a value of 10

µH for the coupled inductor and 22µH for two

inductors will be acceptable for most applications.

APPLICATIO S I FOR ATIO

Figure 2. Suggested Layout

Capacitor Selection

Ceramic capacitors are recommended. An X7R or X5R

dielectric should be used to avoid capacitance decreasing

severely with applied voltage and at temperature limits.

The “flying” capacitor between the SW and D pins should

be a ceramic type of value 1

µF or more. When used in the

dual inductor or coupled inductor topologies the flying

capacitor should have a voltage rating that is more than the

difference between the input and output voltages. For the

charge pump inverter topology, the voltage rating should

be more than the output voltage. The output capacitor

should be a ceramic type. Acceptable output capacitance

varies from 1

(–5V). The input capacitor should be a 1

µF ceramic type

and be placed as close as possible to the LT3462/LT3462A.

Layout Hints

The high speed operation of the LT3462 demands careful

attention to board layout. You will not get advertised

performance with careless layout. Figure 2 shows the

recommended component placement. A ceramic capaci-

tor of 1

µF or more must be placed close to the IC for input

supply bypassing.