LTC3547B datasheet(8/16 Pages) LINER

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LTC3547B

3547bfb

APPLICATIO S I FOR ATIO

A general LTC3547B application circuit is shown in

Figure 1. External component selection is driven by the

load requirement, and begins with the selection of the

inductor L. Once the inductor is chosen, CIN and COUT

can be selected.

Inductor Selection

Although the inductor does not inﬂuence the operat-

ing frequency, the inductor value has a direct effect on

ripple current. The inductor ripple current ΔIL decreases

with higher inductance and increases with higher VIN

or VOUT:

IL =

VOUT

fO • L

•1

VOUT

VIN

(1)

Accepting larger values of ΔIL allows the use of low

inductances, but results in higher output voltage ripple,

greater core losses, and lower output current capability.

A reasonable starting point for setting ripple current

is 40% of the maximum output load current. So, for a

300mA regulator, ΔIL = 120mA (40% of 300mA).

Inductor Core Selection

Different core materials and shapes will change the

size/current and price/current relationship of an induc-

tor. Toroid or shielded pot cores in ferrite or permalloy

materials are small and do not radiate much energy, but

generally cost more than powdered iron core inductors

with similar electrical characteristics. The choice of which

style inductor to use often depends more on the price vs

size requirements, and any radiated ﬁeld/EMI requirements,

than on what the LTC3547B requires to operate. Table 1

shows some typical surface mount inductors that work

well in LTC3547B applications.

Figure 1. LTC3547B General Schematic

CF2

CF1

VIN

2.5V TO 5.5V

VOUT2

VOUT1

3547b F01

COUT2

COUT1

VIN

RUN2

RUN1

LTC3547B

VFB2

SW2

SW1

VFB1

GND

Table 1. Representative Surface Mount Inductors

MANU-

FACTURER

PART NUMBER

VALUE

MAX DC

CURRENT

DCR

HEIGHT

Taiyo Yuden

CB2016T2R2M

CB2012T2R2M

CB2016T3R3M

2.2μH

3.3μH

510mA

530mA

410mA

0.13Ω

0.33Ω

0.27Ω

1.6mm

1.25mm

1.6mm

Panasonic

ELT5KT4R7M

4.7μH

950mA

0.2Ω

1.2mm

Sumida

CDRH2D18/LD

4.7μH

630mA

0.086Ω

2mm

Murata

LQH32CN4R7M23

4.7μH

450mA

0.2Ω

2mm

Taiyo Yuden

NR30102R2M

NR30104R7M

2.2μH

4.7μH

1100mA

750mA

0.1Ω

0.19Ω

1mm

FDK

FDKMIPF2520D

4.7μH

3.3μH

2.2μH

1100mA

1200mA

1300mA

0.11Ω

0.1Ω

0.08Ω

1mm

TDK

VLF3010AT4R7-

MR70

VLF3010AT3R3-

MR87

VLF3010AT2R2-

M1RD

4.7μH

3.3μH

2.2μH

700mA

870mA

1000mA

0.24Ω

0.17Ω

0.12Ω

1mm

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