LT1376CS datasheet(12/28 Pages) LINER

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LT1375/LT1376

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

SERIES

CORE

VENDOR/

VALUE

CORE

RESIS-

MATER-

HEIGHT

PART NO.

(

µH) (Amps) TYPE TANCE(Ω)

IAL

(mm)

Coiltronics

CTX5-1

2.3

Tor

0.027

4.2

CTX10-1

1.9

Tor

0.039

4.2

CTX20-1

1.0

Tor

0.137

4.2

CTX15-2

1.8

Tor

0.058

6.0

CTX20-3

1.5

Tor

0.093

4.7

CTX20-4

2.2

Tor

0.059

6.4

CTX5-1P

1.8

Tor

0.021

4.2

CTX10-1P

1.6

Tor

0.030

4.2

CTX15-1P

1.2

Tor

0.046

4.2

CTX20-1P

1.0

Tor

0.081

4.2

CTX20-2P

1.3

Tor

0.052

6.0

CTX20-4P

1.8

Tor

0.039

6.35

Sumida

CDRH64

1.7

0.084

Fer

4.5

CDRH74

1.2

0.077

Fer

4.5

CDRH73

1.7

0.055

Fer

3.4

CDRH73

1.1

0.15

Fer

3.4

CD73

1.4

Open

0.062

Fer

3.5

CD73

1.1

Open

0.085

Fer

3.5

CD104

2.4

Open

0.041

Fer

4.0

CD104

1.7

Open

0.062

Fer

4.0

Gowanda

SM20-102K

1.3

Open

0.038

Fer

7.0

SM20-152K

1.3

Open

0.049

Fer

7.0

SM20-222K

1.3

Open

0.059

Fer

7.0

Dale

IHSM-4825

3.1

Open

0.071

Fer

5.6

IHSM-4825

1.7

Open

0.152

Fer

5.6

IHSM-5832

4.3

Open

0.053

Fer

7.1

IHSM-5832

2.8

Open

0.12

Fer

7.1

IHSM-7832

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

µ = Kool Mµ

Output Capacitor

The output capacitor is normally chosen by its Effective

Series Resistance (ESR), because this is what determines

output ripple voltage. At 500kHz, any polarized capacitor

is essentially resistive. To get low ESR takes

volume, so

physically smaller capacitors have high ESR. The ESR

range for typical LT1376 applications is 0.05

Ω to 0.5Ω. A

typical output capacitor is an AVX type TPS, 100

µF at 10V,

with a guaranteed ESR less than 0.1

Ω. 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

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

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

µF 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

AVX TAJ

0.9 to 2.0

0.36 to 0.24

C Case Size

AVX TPS

0.2 (typ)

0.5 (typ)

AVX TAJ

1.8 to 3.0

0.22 to 0.17

B Case Size

AVX TAJ

2.5 to 10

0.16 to 0.08

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

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