SC122 Ver la hoja de datos (PDF) - Semtech Corporation
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SC122 Datasheet PDF : 13 Pages
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SC122
Applications Information (continued)
5×f . Any inductor with these properties should provide
osc
satisfactory performance.
The following table lists the manufacturers of recom-
mended inductor options.
PCB Layout Considerations
Good layout can enhance the performance of the DC-DC
converter and can avoid EMI problems, ground bounce,
and resistive voltage losses. The recommended layout is
shown in Figure 2.
Manufacturer/ Value DCR
Part #
(μH) (mΩ)
Rated
Current
(mA)
Tolerance
(%)
Dimensions
L×W×H
(mm)
Sumida 5508472xxxx 4.7 3800
90
2/5/10/20 2.2 × 1.4 × 1.6
Murata
LQM31PN4R7M00L
4.7 300
700
20
3.2 × 1.6 × 0.85
Capacitor Selection
Low ESR capacitors such as X5R or X7R type ceramic
capacitors are recommended for input bypassing and
output filtering. Low-ESR tantalum capacitors are not rec-
ommended due to possible reduction in capacitance seen
at the switching frequency of the SC122. Ceramic capaci-
tors of type Y5V are not recommended as their tempera-
ture coefficients make them unsuitable for this
application.
The input and output each require a minimum capaci-
tance value of 10μF at the programmed output voltage.
This must be considered when choosing small package
size capacitors as the DC bias must be included in their
derating to ensure this required value. For example, a
10μF 0805 capacitor may provide sufficient capacitance at
low output voltages but may be too low at higher output
voltages. Therefore, a higher nominal capacitance value
may be required to provide the minimum of 10μF at these
higher output voltages. Additional output capacitance
can be used extend the time between bursts, or to improve
load transient response. The following table lists recom-
mended capacitors.
The following simple design rules can be implemented to
ensure good layout:
• Place the inductor and filter capacitors as close
to the device as possible and use short wide
traces between the power components.
• Maximize ground metal on the component side
to improve the return connection and thermal
dissipation. Separation between the LX node
and GND should be maintained to avoid cou-
pling capacitance between the LX node and the
ground plane.
• Use a ground plane with several vias connecting
to the component side ground to further reduce
noise interference on sensitive circuit nodes.
6.7mm
COUT
VOUT
LX
LX
OUT
GND SC122 GND
IN
EN
5.2mm
CIN
GND
Manufacturer/
Part Number
Murata
GRM21BR60J226ME39B
Murata
GRM31CR71A226KE15L
Value
(μF)
Rated Voltage
(VDC)
Type
Case
Size
22
6.3
X5R 0805
22
10
X7R 1206
Figure 2 — Recommended Layout
11
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