LT1576CS8-SYNC 查看數據表（PDF） - Linear Technology

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LT1576CS8-SYNC

1.5A, 200kHz Step-Down Switching Regulator

Linear Technology 

LT1576/LT1576-5

APPLICATIONS INFORMATION

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

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

Output Capacitor

The output capacitor is normally chosen by its Effective

Series Resistance (ESR), because this is what determines

output ripple voltage. To get low ESR takes volume, so

physically smaller capacitors have high ESR. The ESR

range for typical LT1576 applications is 0.05Ω to 0.2Ω. A

typical output capacitor is an AVX type TPS, 100µF at 10V,

with a guaranteed ESR less than 0.1Ω. This is a “D” size

surface mount solid tantalum capacitor. TPS capacitors

are specially constructed and tested for low ESR, so they

give the lowest ESR for a given volume. The value in

microfarads is not particularly critical, and values from

22µF to greater than 500µF work well, but you cannot

cheat mother nature on ESR. If you find a tiny 22µF solid

tantalum capacitor, it will have high ESR, and output ripple

voltage will be terrible. Table 3 shows some typical solid

tantalum surface mount capacitors.

Table 3. Surface Mount Solid Tantalum Capacitor ESR

and Ripple Current

E Case Size

ESR (Max., Ω) Ripple Current (A)

AVX TPS, Sprague 593D

0.1 to 0.3

0.7 to 1.1

AVX TAJ

0.7 to 0.9

0.4

D Case Size

AVX TPS, Sprague 593D

0.1 to 0.3

0.7 to 1.1

C Case Size

AVX TPS

0.2 (typ)

0.5 (typ)

Many engineers have heard that solid tantalum capacitors

are prone to failure if they undergo high surge currents.

This is historically true, and type TPS capacitors are

specially tested for surge capability, but surge ruggedness

is not a critical issue with the output capacitor. Solid

tantalum capacitors fail during very high turn-on surges,

which do not occur at the output of regulators. High

discharge surges, such as when the regulator output is

dead shorted, do not harm the capacitors.

Unlike the input capacitor, RMS ripple current in the

output capacitor is normally low enough that ripple cur-

rent rating is not an issue. The current waveform is

triangular with a typical value of 200mARMS. The formula

to calculate this is:

12

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