Rainbow-electronics MAX8640Z Bedienungsanleitung PDF herunterladen (Seite 6)

Soft-Start

The MAX8640Y/MAX8640Z include internal soft-start

circuitry that eliminates inrush current at startup, reduc-

ing transients on the input source. Soft-start is particu-

larly useful for higher impedance input sources, such

as Li+ and alkaline cells. See the Soft-Start Response

in the Typical Operating Characteristics.

Applications Information

The MAX8640Y/MAX8640Z are optimized for use with a

tiny inductor and small ceramic capacitors. The correct

selection of external components ensures high efficien-

cy, low output ripple, and fast transient response.

Inductor Selection

A 1µH inductor is recommended for use with the

MAX8640Z, and 2.2µH is recommended for the

MAX8640Y. A 1µH inductor is physically smaller but

requires faster switching, resulting in some efficiency

loss. Table 1 lists several recommended inductors.

It is acceptable to use a 1.5µH inductor with either the

MAX8640Y or MAX8640Z, but efficiency and ripple

should be verified. Similarly, it is acceptable to use a

3.3µH inductor with the MAX8640Y, but performance

should be verified.

For optimum voltage positioning of load transients,

choose an inductor with DC series resistance in the

75mΩ to 150mΩ range. For higher efficiency at heavy

loads (above 200mA) or minimal load regulation (but

some transient overshoot), the resistance should be

kept as low as possible. For light-load applications up

to 200mA, higher resistance is acceptable with very lit-

tle impact on performance.

MAX8640Y/MAX8640Z

500mA, 4MHz/2MHz Synchronous

Step-Down DC-DC Converters in SC70

6 _______________________________________________________________________________________

Table 1. Suggested Inductors

MANUFACTURER SERIES

INDUCTANCE

(µH)

DC RESISTANCE

(Ω typ)

CURRENT RATING

(mA)

DIMENSIONS

L x W x H (mm)

MIPFT2520D 2.0 0.16 900 2.5 x 2.0 x 0.5

1.5 0.07 1500

2.2 0.08 1300

FDK

MIPF2520D

3.3 0.10 1200

2.5 x 2.0 x 1.0

1.0 0.12 1200

1.5 0.16 1000Murata LQM31P

2.2 0.22 900

3.2 x 1.6 x 0.95

1.2 0.08 590

1.5 0.09 520

Sumida CDRH2D09

2.2 0.12 440

3.0 x 3.0 x 1.0

1.0 0.11 1100

1.5 0.13 1000

Taiyo Yuden CKP3216T

2.2 0.14 900

3.2 x 1.6 x 0.9

1.0 0.15 460

GLF201208T

2.2 0.36 300

2.0 x 1.25 x 0.9

1.0 0.07 400

GLF2012T

2.2 0.10 300

2.0 x 1.25 x 1.35

1.0 0.10 800

TDK

GLF251812T

2.2 0.20 600

2.5 x 1.8 x 1.35

1.0 0.05 1000

MDT2520-CR

2.2 0.08 700

2.5 x 2.0 x 1.0

1.0 0.07 1100

TOKO

D2812C

2.2 0.14 770

2.8 x 2.8 x 1.2

1 2 3 4 5 6 7 8 9

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