MP2355 データシートの表示（PDF） - Monolithic Power Systems

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MP2355

3A, 23V, 380KHz Step-Down Converter

Monolithic Power Systems 

TM

MP2355 – 3A, 23V, 380KHz STEP-DOWN CONVERTER

Table 1—Inductor Selection Guide

Vendor/

Model

Core

Type

Sumida

CR75

Open

CDH74

Open

CDRH5D28 Shielded

CDRH5D28 Shielded

Sumida (continued)

CDRH6D28 Shielded

CDRH104R Shielded

Toko

D53LC

Type A

Shielded

D75C Shielded

D104C Shielded

D10FL

Open

Coilcraft

DO3308

Open

DO3316

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

Output Rectifier Diode

The output rectifier diode supplies the current to

the inductor when the high-side switch is off. To

reduce losses due to the diode forward voltage

and recovery times, use a Schottky diode.

Choose a diode which has a maximum reverse

voltage rating is greater than the maximum

input voltage, and who’s current rating is

greater than the maximum load current. Table 2

lists example Schottky diodes and

manufacturers.

Table 2—Diode Selection Guide

Diode

SK33

SK34

B330

B340

MBRS330

MBRS340

Voltage/Current Manufacture

Rating

30V, 3A Diodes Inc.

40V, 3A Diodes Inc.

30V, 3A Diodes Inc.

40V, 3A Diodes Inc.

30V, 3A On Semiconductor

40V, 3A On Semiconductor

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.

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 at VIN = 2VOUT,

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 × VOUT

fs × C1 VIN

× ⎜⎜⎝⎛1 −

VOUT

VIN

⎟⎟⎠⎞

MP2355 Rev. 1.5

www.MonolithicPower.com

7

5/1/2006

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2006 MPS. All Rights Reserved.

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