8

LTC3410

3410fb

The basic LTC3410 application circuit is shown in Figure 1.

External component selection is driven by the load require-

Inductor Selection

For most applications, the value of the inductor will fall in

the range of 2.2

µH to 4.7µH. Its value is chosen based on

the desired ripple current. Large value inductors lower

ripple current and small value inductors result in higher

current as shown in equation 1. A reasonable starting point

for setting ripple current is

−

⎛

⎝⎜

⎞

⎠⎟

I

fL

V

V

V

L

OUT

OUT

IN

1

11

()

The DC current rating of the inductor should be at least

equal to the maximum load current plus half the ripple

current to prevent core saturation. Thus, a 360mA rated

inductor should be enough for most applications (300mA

+ 60mA). For better efficiency, choose a low DC-resistance

inductor.

The inductor value also has an effect on Burst Mode

operation. The transition to low current operation begins

when the inductor current peaks fall to approximately

100mA. Lower inductor values (higher

to occur at lower load currents, which can cause a dip in

efficiency in the upper range of low current operation. In

Burst Mode operation, lower inductance values will cause

the burst frequency to increase.

APPLICATIO S I FOR ATIO

Inductor Core Selection

Different core materials and shapes will change the size/

current and price/current relationship of an inductor. Tor-

oid or shielded pot cores in ferrite or permalloy materials

are small and don’t radiate much energy, but generally cost

more than powdered iron core inductors with similar

electrical characteristics. The choice of which style induc-

tor to use often depends more on the price vs size require-

ments and any radiated field/EMI requirements than on

what the LTC3410 requires to operate. Table 1 shows some

typical surface mount inductors that work well in

LTC3410 applications.

Table 1. Representative Surface Mount Inductors

MAX DC

MANUFACTURER PART NUMBER

VALUE CURRENT DCR HEIGHT

Taiyo Yuden

CB2016T2R2M

2.2

µH 510mA 0.13Ω 1.6mm

CB2012T2R2M

2.2

µH 530mA 0.33Ω 1.25mm

LBC2016T3R3M

3.3

µH 410mA 0.27Ω 1.6mm

Panasonic

ELT5KT4R7M

4.7

µH 950mA 0.2Ω 1.2mm

Sumida

CDRH2D18/LD

4.7

µH 630mA 0.086Ω 2mm

Murata

LQH32CN4R7M23 4.7

µH 450mA 0.2Ω 2mm

Taiyo Yuden

NR30102R2M

2.2

µH 1100mA 0.1Ω 1mm

NR30104R7M

4.7

µH 750mA 0.19Ω 1mm

FDK

FDKMIPF2520D

4.7

µH 1100mA 0.11Ω 1mm

FDKMIPF2520D

3.3

µH 1200mA 0.1Ω 1mm

FDKMIPF2520D

2.2

µH 1300mA 0.08Ω 1mm

In continuous mode, the source current of the top MOSFET

voltage transients, a low ESR input capacitor sized for the

maximum RMS current must be used. The maximum

RMS capacitor current is given by:

C

required I

I

VV

V

V

IN

RMS

OMAX

OUT

IN

OUT

IN

≅

−

()

monly used for design because even significant deviations

do not offer much relief. Note that the capacitor

manufacturer’s ripple current ratings are often based on

4.7

µF

CER

2.7V

TO 5.5V

LTC3410

RUN

4.7

µH

10pF

232k

464k

3410 F01

SW

GND

4.7

µF

CER

1.2V

Figure 1. High Efficiency Step-Down Converter