Rainbow Electronics MAX8640Z - Manual (Page 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
75m
Ω 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 1000 Murata 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