Rainbow-electronics MAX1724 Manual de usuario descargar pdf (Pagina 9)

MAX1722/MAX1723/MAX1724

1.5µA I

, Step-Up DC-DC Converters

in Thin SOT23-5

_______________________________________________________________________________________ 9

Inductor Selection

The control scheme of the MAX1722/MAX1723/

MAX1724 permits flexibility in choosing an inductor. A

10µH inductor value performs well in most applications.

Smaller inductance values typically offer smaller physi-

cal size for a given series resistance, allowing the

smallest overall circuit dimensions. Circuits using larger

inductance values may start up at lower battery volt-

ages, provide higher efficiency, and exhibit less ripple,

but they may reduce the maximum output current. This

occurs when the inductance is sufficiently large to pre-

vent the maximum current limit (I

LIM

) from being

reached before the maximum on-time (t

ON(MAX)

)

expires.

For maximum output current, choose the inductor value

so that the controller reaches the current-limit before

the maximum on-time is triggered:

where the maximum on-time is typically 5µs, and the

current limit (I

LIM

) is typically 500mA (see Electrical

Characteristics table).

For larger inductor values, determine the peak inductor

current (I

PEAK)

by:

The inductor’s incremental saturation current rating should

be greater than the peak switching current. However, it is

generally acceptable to bias the inductor into saturation

by as much as 20%, although this will slightly reduce effi-

ciency. Table 1 lists suggested inductors and suppliers.

Maximum Output Current

The maximum output current depends on the peak induc-

tor current, the input voltage, the output voltage, and the

overall efficiency (η):

OUT MAX PEAK

BATT

OUT

()













PEAK

BATT ON MAX

()

BATT ON MAX

LIM

()

MAX1724

GND

BATT

OUTPUT

OUT (NOM)

INPUT

0.8V TO V

OUT

10µH

10µF

SHDN

OUT

10µF

OFF

Figure 8. MAX1724 Standard Application Circuit

Table 1. Suggested Inductors and

Suppliers

MAX1722

GND

BATT

OUTPUT

2V TO 5.5V

INPUT

0.8V TO V

OUT

Figure 7. Adjustable Output Circuit

MANUFACTURER INDUCTOR

PHONE

WEBSITE

Coilcraft

DO1608 Series

DO1606 Series

847-639-2361

www.coilcraft.com

Murata LQH4C Series

770-436-1300

www.murata.com

Sumida

CDRH4D18 Series

CR32 Series

CMD4D06 Series

847-545-6700

www.sumida.com

Sumitomo/

Daidoo Electronics

CXLD140 Series

+81 (06) 6355-5733

www.daidoo.co.jp

Toko

3DF Type

D412F Type

847-297-0070

www.toko.com

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Rainbow-electronics MAX1724 Manual de usuario Pagina 9

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