1506F 查看數據表（PDF） - Linear Technology

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1506F

4.5A, 500kHz Step-Down Switching Regulator

Linear Technology 

LT1506

APPLICATIONS INFORMATION

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 = Semiclosed 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. 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 LT1506 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:

Output Capacitor Ripple Current (RMS):

( ( )())(( ) ) ( ) IRIPPLE RMS

0.29

=

VOUT

Lf

VIN − VOUT

VIN

11

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