LT1578 データシートの表示（PDF） - Linear Technology

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LT1578

1.5A, 200kHz Step-Down Switching Regulator

Linear Technology 

LT1578/LT1578-2.5

APPLICATIONS INFORMATION

(()( )( ) ) IPEAK

=

IOUT

+

VOUT

2

VIN

fL

− VOUT

VIN

VIN = Maximum input voltage

f = Switching frequency, 200kHz

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 1) 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 1

VENDOR/

PART NO.

SERIES CORE

VALUE DC CORE RESIS- MATER- HEIGHT

(µH) (Amps) TYPE TANCE(Ω) IAL (mm)

Coiltronics

CTX15-2

15 1.7 Tor 0.059 KMµ 6.0

CTX33-2

33 1.4 Tor 0.106 KMµ 6.0

CTX68-4

68 1.2 Tor 0.158 KMµ 6.4

CTX15-1P

15 1.4 Tor 0.087

52

4.2

CTX33-2P

33 1.3 Tor 0.126

52

6.0

CTX68-4P

68 1.1 Tor 0.238

52

6.4

Sumida

CDRH74-150

15 1.47 SC 0.081

Fer

4.5

CDH115-330

33 1.68 SC 0.082

Fer

5.2

CDRH125-680 68 1.5 SC 0.12

Fer

6

CDH74-330

33 1.45 SC 0.17

Fer

5.2

Coilcraft

DO3308P-153 15

2

SC

0.12

Fer

3

DO3316P-333 33

2

SC

0.1

Fer 5.21

DO3316P-683 68 1.4 SC 0.18

Fer 5.21

Pulse

PE-53602

35 1.4 Tor 0.166

Fer

9.1

PE-53604

73 1.3 Tor 0.290

Fer

9.1

PE-53632

22 2.7 Tor 0.063

Fer

9.1

PE-53633

40 2.7 Tor 0.085 Fer

10

Gowanda

SMP3316-152K 15 3.5 SC 0.041 Fer

6

SMP3316-332K 33 2.3 SC 0.092 Fer

6

SMP3316-682K 68 1.7 SC 0.178 Fer

6

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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