MP2354DS-LF-Z データシートの表示（PDF） - Monolithic Power Systems

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MP2354DS-LF-Z

2A, 23V, 380KHz Step-Down Converter

Monolithic Power Systems 

TM

MP2354 – 2A, 23V, 380KHz STEP-DOWN CONVERTER

Table 1 lists a number of suitable inductors

from various manufacturers. The choice of

which style inductor to use mainly depends on

the price vs. size requirements and any EMI

requirement.

Table 1—Inductor Selection Guide

Vendor/

Model

Sumida

CR75

CDH74

CDRH5D28

CDRH5D28

CDRH6D28

CDRH104R

Toko

D53LC

Type A

D75C

D104C

D10FL

Coilcraft

DO3308

DO3316

Core

Type

Open

Open

Shielded

Shielded

Shielded

Shielded

Shielded

Shielded

Shielded

Open

Open

Open

Core

Material

Ferrite

Ferrite

Ferrite

Ferrite

Ferrite

Ferrite

Ferrite

Ferrite

Ferrite

Ferrite

Ferrite

Ferrite

Package

Dimensions

(mm)

WL H

7.0 7.8 5.5

7.3 8.0 5.2

5.5 5.7 5.5

5.5 5.7 5.5

6.7 6.7 3.0

10.1 10.0 3.0

5.0 5.0 3.0

7.6 7.6 5.1

10.0 10.0 4.3

9.7 1.5 4.0

9.4 13.0 3.0

9.4 13.0 5.1

Input Capacitor

The input current to the step-down converter is

discontinuous, therefore a capacitor is required

to supply the AC current to the step-down

converter while maintaining the DC input

voltage. Use low ESR capacitors for the best

performance. Ceramic capacitors are preferred,

but tantalum or low-ESR electrolytic capacitors

may also suffice. Choose X5R or X7R

dielectrics when using ceramic capacitors.

Since the input capacitor (C1) absorbs the input

switching current it requires an adequate ripple

current rating. The RMS current in the input

capacitor can be estimated by:

IC1 = ILOAD ×

VOUT

VIN

×⎜⎜⎛1−

⎝

VOUT

VIN

⎟⎞

⎟

⎠

The worst-case condition occurs where:

IC1

=

ILOAD

2

For simplification, choose the input capacitor

whose RMS current rating greater than half of

the maximum load current.

The input capacitor can be electrolytic, tantalum

or ceramic. When using electrolytic or tantalum

capacitors, a small, high quality ceramic

capacitor, i.e. 0.1µF, should be placed as close

to the IC as possible. When using ceramic

capacitors, make sure that they have enough

capacitance to provide sufficient charge to

prevent excessive voltage ripple at input. The

input voltage ripple caused by capacitance can

be estimated by:

∆VIN

=

ILOAD ×

fS × C1

VOUT

VIN

× ⎜⎜⎝⎛1 −

VOUT

VIN

⎟⎟⎠⎞

Output Capacitor

The output capacitor is required to maintain the

DC output voltage. Ceramic, tantalum, or low

ESR electrolytic capacitors are recommended.

Low ESR capacitors are preferred to keep the

output voltage ripple low. The output voltage

ripple can be estimated by:

∆VOUT

=

VOUT

fS × L

× ⎜⎜⎝⎛1−

VOUT

VIN

⎟⎟⎠⎞ × ⎜⎜⎝⎛RESR

+

8

×

f

1

S×

C2

⎟⎟⎠⎞

Where L is the inductor value, C2 is the output

capacitance value and RESR is the equivalent

series resistance (ESR) value of the output

capacitor.

In the case of ceramic capacitors, the

impedance at the switching frequency is

dominated by the capacitance. The output

voltage ripple is mainly caused by the

capacitance. For simplification, the output

voltage ripple can be estimated by:

∆VOUT

=

VOUT

8 × fS2 × L × C2

× ⎜⎜⎝⎛1−

VOUT

VIN

⎟⎟⎠⎞

In the case of tantalum or electrolytic

capacitors, the ESR dominates the impedance

at the switching frequency. For simplification,

the output ripple can be approximated to:

∆VOUT

=

VOUT

fS × L

×

⎜⎜⎝⎛1 −

VOUT

VIN

⎟⎟⎠⎞ × RESR

The characteristics of the output capacitor also

affect the stability of the regulation system. The

MP2354 Rev. 1.4

www.MonolithicPower.com

7

1/6/2006

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© 2006 MPS. All Rights Reserved.

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