LTC3564 datasheet(9/20 Pages) LINER

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LTC3564

3564f

The basic LTC3564 application circuit is shown in Figure 1.

External component selection is driven by the load require-

ment and begins with the selection of L followed by CIN and

COUT.

Inductor Selection

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

the range of 0.47

μH to 2.2μH. Its value is chosen based on

the desired ripple current. Large value inductors lower

ripple current and small value inductors result in higher

ripple currents. Higher VIN or VOUT also increases the ripple

current as shown in equation 1. A reasonable starting point

for setting ripple current is

ΔIL = 500mA (40% of 1.25A).

Δ = ()( )

−

⎛

⎝⎜

⎞

⎠⎟

OUT

(1)

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 1.5A rated

inductor should be enough for most applications (1.25A

+ 250mA). For better efficiency, choose a low DC-resis-

tance 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

300mA. Lower inductor values (higher

ΔIL) will cause this

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.

Inductor Core Selection

Different core materials and shapes will change the size/

current and price/current relationship of an inductor.

Toroid or shielded pot cores in ferrite or permalloy mate-

rials are small and don’t radiate much energy, but gener-

ally 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 LTC3564 requires to operate. Table 1

shows some typical surface mount inductors that work

well in LTC3564 applications.

APPLICATIO S I FOR ATIO

Table 1. Representative Surface Mount Inductors

MANUFATURER

PART NUMBER

VALUE (

μH)

MAX DC CURRENT (A)

DCR (m

Ω)

HEIGHT (mm)

Toko

A915AY-1R1M-DC53LC

1.1

3.25

1070AS-1R0N-DB3020C

1.9

Sumida

CDRH4D18C/LD-1R1

1.1

2.1

CDRH3D14-1R2

1.2

2.2

1.5

CR5D11-1R0

2.2

1.2

CDRH2D18/HP-2R2

2.2

1.6

FDK

MIPW3226D0R9M

0.9

1.4

Coilcraft

LPO6610-122ML

1.2

2.1

LPS4018-222ML

2.2

2.5

1.8

Vishay

IHLP1616ABERR47M01

0.47

1.2

IHLP1616ABER1R0M01

1.2

VIN

LTC3564

RUN

3564 F01

CIN

COUT

VIN

VOUT

VFB

GND

Figure 1. LTC3564 General Schematic

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