LTC3619B datasheet(11/20 Pages) LINER

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LTC3619B

3619bfa

AgeneralLTC3619BapplicationcircuitisshowninFigure2.

Externalcomponentselectionisdrivenbytheloadrequire-

ment, 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:

ΔIL =

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 800mA

regulator,

ΔIL = 320mA (40% of 800mA).

The inductor value will also have an effect on Burst Mode

operation. The transition to low current operation begins

when the peak inductor current falls below a level set by

the internal burst clamp. Lower inductor values result in

higher ripple current which causes the transition to occur

at lower load currents. This causes a dip in efficiency in

the upper range of low current operation. Furthermore,

lower inductance values will cause the bursts to occur

with increased frequency.

Inductor Core Selection

Differentcorematerialsandshapeswillchangethesize/cur-

rent and price/current relationship of an inductor. 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 induc-

tor to use often depends more on the price versus size

requirements, and any radiated field/EMI requirements,

than on what the LTC3619B requires to operate. Table 1

shows some typical surface mount inductors that work

well in LTC3619B applications.

Table 1. Representative Surface Mount Inductors

MANU-

FACTURER

PART NUMBER VALUE

MAX DC

CURRENT

DCR

HEIGHT

Coilcraft

LPS4012-152ML

LPS4012-222ML

LPS4012-332ML

LPS4012-472ML

LPS4018-222ML

LPS4018-332ML

LPS4018-472ML

1.5µH

2.2µH

3.3µH

4.7µH

2.2µH

3.3µH

4.7µH

2200mA

1750mA

1450mA

2300mA

2000mA

1800mA

0.070Ω

0.100Ω

0.170Ω

0.070Ω

0.080Ω

0.125Ω

1.2mm

1.8mm

FDK

FDKMIPF2520D

4.7µH

3.3µH

2.2µH

1100mA

1200mA

1300mA

0.11Ω

0.1Ω

0.08Ω

1mm

Murata

LQH32CN4R7M23 4.7µH

450mA

0.2Ω

2mm

Panasonic ELT5KT4R7M

4.7µH

950mA

0.2Ω

1.2mm

Sumida

CDRH2D18/LD

CDH38D11SNP-

3R3M

CDH38D11SNP-

2R2M

4.7µH

3.3μH

2.2μH

630mA

1560mA

1900mA

0.086Ω

0.115Ω

0.082Ω

2mm

1.2mm

Taiyo Yuden CB2016T2R2M

CB2012T2R2M

CB2016T3R3M

NR30102R2M

NR30104R7M

2.2µH

3.3µH

2.2µH

4.7µH

510mA

530mA

410mA

1100mA

750mA

0.13Ω

0.33Ω

0.27Ω

0.1Ω

0.19Ω

1.6mm

1.25mm

1.6mm

1mm

TDK

VLF3010AT4R7-

MR70

VLF3010AT3R3-

MR87

VLF3010AT2R2-

M1R0

VLF4012AT-2R2

M1R5

VLF5012ST-3R3

M1R7

VLF5014ST-2R2

M2R3

4.7µH

3.3µH

2.2µH

3.3μH

2.2µH

700mA

870mA

1000mA

1500mA

1700mA

2300mA

0.28Ω

0.17Ω

0.12Ω

0.076Ω

0.095Ω

0.059Ω

1mm

1.2mm

1.4mm

VIN

RUN2

RUN1

LTC3619B

VFB2

SW2

SW1

PGOOD1

PGOOD2

VFB1

CF2

CF1

GND

VIN

2.5V TO 5.5V

VOUT2

VOUT1

3619B F02

COUT2

COUT1

RLIM

CLIM

RLIM

Figure 2. LTC3619B General Schematic

applicaTions inForMaTion

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