3.3V/5V or Adjustable-Output,

Single-Cell DC-DC Converters

10

______________________________________________________________________________________

Inductor Selection

An inductor value of 330µH works well in most applica-

tions, supplying loads over 10mA and allowing typical

start-up voltages of 0.8V. The inductor value is not

critical, and the MAX866/MAX867 can operate with val-

ues from 22µH to 1mH. In general, smaller inductor val-

ues supply more output current while larger values start

with lower input voltage. Several inductor suppliers and

part numbers are listed in Tables 1 and 2.

The peak inductor current should not exceed the induc-

tor’s current rating. Since the MAX866/MAX867 current

limit of 0.5A will not be reached in most applications,

so:

which is well within the ratings of most surface-mount

coils. Higher efficiency and output current are achieved

with lower inductor resistance, but unfortunately this is

inversely related to physical size. Table 2 indicates

resistance and height for each coil. Some of the small-

est coils have resistances over 10

Ω, and will not pro-

vide the same output power or efficiency of a 1

Ω coil.

At light loads however (below 5mA), the efficiency dif-

ferences between low- and high-resistance coils may

be only a percent or two. The

Typical Operating

Characteristics graphs show efficiency and output cur-

rent plots for 1.5

Ω and 2.9Ω, 330µH coils.

Capacitor Selection

A 47µF, 6V, 0.85

Ω, surface-mount tantalum (SMT)

output filter capacitor typically provides 15mV output

ripple when stepping up from 0.9V to 1.4V at 10mA.

Smaller capacitors (down to 10µF with higher ESRs) are

acceptable for light loads or in applications that can

Table 1. Component Suppliers

(847) 390-4405

USA:

(847) 390-4461

TDK

(805) 867-2698

81-3-3494-7414

USA:

(805) 867-2555

Japan: 81-3-3494-7411

Nihon

(847) 639-1469

USA:

(847) 639-6400

Coilcraft

(310) 515-1962

USA:

(310) 515-1720

J.W. Miller

(847) 956-0702

81-3-3607-5144

USA:

(847) 956-0666

Japan: 81-3-3607-5111

Sumida

(619) 661-1055

81-7-2070-1174

USA:

(619) 661-6835

Japan: 81-7-2070-6306

Sanyo

(814) 238-0490

USA:

(800) 831-9172

Murata-Erie

(602) 244-4015

USA:

(602) 244-5303

Motorola

(714) 960-6492

USA:

(714) 969-2491

Matsuo

(803) 626-3123

USA:

(803) 946-0690

AVX

FAX

PHONE

COMPANY

PRODUCTION

METHOD

INDUCTORS

CAPACITORS

Surface Mount

See Table 2

Matsuo 267 series

Sprague 595D series

AVX TPS series

Motorola MBR 0530

Nihon EC15QS02L

Miniature

Through Hole

Sumida

RCH654-220

Sanyo

OS-CON series

low-ESR organic

semiconductor

Motorola 1N5017

RECTIFIERS