SC4541EVB-2 データシートの表示（PDF） - Semtech Corporation
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SC4541EVB-2
Semtech Corporation
SC4541EVB-2 Datasheet PDF : 19 Pages
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SC4541
Applications Information ( continued)
The converter has higher efficiency under CCM and the
inductor peak current is calculated by the following
equation.
IL _ PEAK
IIN
VIN u D
2 u FS u L
Assuming CCM, the duty ratio is calculated using the fol-
lowing equation.
D VOUT VIN VD
VOUT VD
VD is the forward voltage drop of the internal Schottky
rectifier.
A 1µF ceramic input and output capacitor should be ade-
quate for most applications. Larger capacitance reduces
voltage ripple, overshoot and undershoot during load
transient as well as improving loop stability margin.
Recommended ceramic capacitor manufacturers are
listed in Table 1.
Table 2 — Recommended Ceramic Capacitor
Manufacturers
Vendor
Kemet
Phone
408-986-0424
Website
www.kemet.com
Murata
814-237-1431
www.murata.com
Taiyo Yuden
408-573-4150
www.t-yuden.com
The inductor ripple current is further shown by the follow-
ing equation.
IL _ RIPPLE
VIN u D
FS u L
The recommended inductance shown in Table 1 is based
on operation with regulated 5V input, dual Li-ion or three
Li-ion battery packs. Increased inductance is required for
higher input and output voltage configurations.
Table 1 — Inductance Requirements, Driving 6 bWLED
Input Type
Input Voltage
Range
L1 Induc-
tance
Regulated 5V
4.5 to 5.5V
10µH
Dual Lithium Ion Battery Pack
5.4 to 8.4V
22µH
Three Lithium Ion Battery Pack
8.1 to 12.6V
33µH
Output Capacitor Selection
Ceramic capacitors are placed near IN and OUT pins to
ground in order to minimize ripple voltage. The minimum
capacitance needed for a given ripple can be estimated
using the following equation.
COUT
VOUT VIN u IOUT
VOUT u FS u VRIPPLE
VRIPPLE = Peak to peak output voltage ripple
IOUT = Output current
VOUT = Boost output voltage
VIN = Input voltage
FS = Switching frequency
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