MAX866/MAX867
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,
the peak coil current (I
PK
) is:
I
PK
= (V
IN(max)
x 4.5µs) / L
For a typical 1-cell alkaline design, V
IN(max)
is 1.55V,
so:
I
PK
= (1.55V x 4.5µs) / 330µH = 21.14mA
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 10Ω, and will not pro-
vide the same output power or efficiency of a 1Ω 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 1.5Ω and 2.9Ω, 330µH coils.
Capacitor Selection
A 47µF, 6V, 0.85Ω, 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) 390-4405USA: (847) 390-4461TDK
(805) 867-2698
81-3-3494-7414
USA: (805) 867-2555
Japan: 81-3-3494-7411
Nihon
(847) 639-1469USA: (847) 639-6400Coilcraft
(310) 515-1962USA: (310) 515-1720J.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) 238-0490USA: (800) 831-9172Murata-Erie
(602) 244-4015USA: (602) 244-5303Motorola
(714) 960-6492USA: (714) 969-2491Matsuo
(803) 626-3123USA: (803) 946-0690AVX
FAXPHONECOMPANY
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
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