LT1374IT7(RevA) データシートの表示（PDF） - Linear Technology

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LT1374IT7
(Rev.:RevA)

4.5A, 500kHz Step-Down Switching Regulator

Linear Technology 

LT1374

APPLICATIONS INFORMATION

saturate abruptly. Other core materials fall somewhere

in between. The following formula assumes continu-

ous mode of operation, but it errs only slightly on the

high side for discontinuous mode, so it can be used for

all conditions.

(()( )( ) ) IPEAK

=

IOUT

+

VOUT

2

VIN

fL

− VOUT

VIN

VIN = Maximum input voltage

f = Switching frequency, 500kHz

3. Decide if the design can tolerate an “open” core geom-

etry like a rod or barrel, with high magnetic field

radiation, or whether it needs a closed core like a toroid

to prevent EMI problems. One would not want an open

core next to a magnetic storage media, for instance!

This is a tough decision because the rods or barrels are

temptingly cheap and small and there are no helpful

guidelines to calculate when the magnetic field radia-

tion will be a problem.

4. Start shopping for an inductor (see representative

surface mount units in Table 2) which meets the

requirements of core shape, peak current (to avoid

saturation), average current (to limit heating), and fault

current (if the inductor gets too hot, wire insulation will

melt and cause turn-to-turn shorts). Keep in mind that

all good things like high efficiency, low profile, and high

temperature operation will increase cost, sometimes

dramatically. Get a quote on the cheapest unit first to

calibrate yourself on price, then ask for what you really

want.

5. After making an initial choice, consider the secondary

things like output voltage ripple, second sourcing, etc.

Use the experts in the Linear Technology’s applica-

tions department if you feel uncertain about the final

choice. They have experience with a wide range of

inductor types and can tell you about the latest devel-

opments in low profile, surface mounting, etc.

Table 2

VENDOR/

PART NO.

SERIES CORE

VALUE DC CORE RESIS- MATER- HEIGHT

(µH) (Amps) TYPE TANCE(Ω) IAL (mm)

Coiltronics

CTX2-1

2

4.1 Tor 0.011 KMµ

4.2

CTX5-4

5

4.4 Tor 0.019 KMµ

6.4

CTX8-4

8

3.5 Tor 0.020 KMµ

6.4

CTX2-1P

2

3.4 Tor 0.014

52

4.2

CTX2-3P

2

4.6 Tor 0.012

52

4.8

CTX5-4P

5

3.3 Tor 0.027

52

6.4

Sumida

CDRH125

10 4.0 SC 0.025

Fer

6

CDRH125

12 3.5 SC 0.027

Fer

6

CDRH125

15 3.3 SC 0.030

Fer

6

CDRH125

18 3.0 SC 0.034

Fer

6

Coilcraft

DT3316-222 2.2

5

SC 0.035

Fer

5.1

DT3316-332 3.3

5

SC 0.040

Fer

5.1

DT3316-472 4.7

3

SC 0.045

Fer

5.1

Pulse

PE-53650

4

4.8 Tor 0.017

Fer

9.1

PE-53651

5

5.4 Tor 0.018

Fer

9.1

PE-53652

9

5.5 Tor 0.022

Fer

10

PE-53653

16 5.1 Tor 0.032

Fer

10

Dale

IHSM-4825 2.7 5.1 Open 0.034

Fer

5.6

IHSM-4825 4.7 4.0 Open 0.047

Fer

5.6

IHSM-5832 10 4.3 Open 0.053

Fer

7.1

IHSM-5832 15 3.5 Open 0.078

Fer

7.1

IHSM-7832 22 3.8 Open 0.054

Fer

7.1

Tor = Toroid

SC = Semi-closed geometry

Fer = Ferrite core material

52 = Type 52 powdered iron core material

KMµ = Kool Mµ

11

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