sc120skevb Semtech Corporation, sc120skevb Datasheet - Page 26

• Manufacturer Part Number: sc120skevb
• Description: Low Voltage Synchronous Boost Regulator
• Manufacturer: Semtech Corporation

Applications Information (continued)
L = 4.7μH should perform well for most applications. For
high V
above), L = 6.8μH, along with a larger output capacitance
or larger-package output capacitor (for better V-bias per-
formance), will ensure correct mode–switching behavior.
For very low V
nearly-depleted single-cell alkaline battery), a smaller
value of inductance will help to ensure that PWM mode
will switch to PSAVE mode as the load decreases. This
consideration may be of little importance in most applica-
tions, as there is little energy remaining in such a deeply
discharged battery.
The following table lists the manufacturers of recom-
mended inductor options.
Capacitor Selection
Input and output capacitors must be chosen carefully to
ensure that they are of the correct value and rating. The
output capacitor requires a minimum capacitance value
of 10μF at the programmed output voltage to ensure sta-
bility over the full operating range. This must be consid-
ered 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 suffi cient capacitance at low output voltages but
may be too low at higher output voltages. Therefore, a
higher capacitance value may be required to provide the
minimum of 10μF at these higher output voltages.
Additional output capacitance may be required for V
close to V
stability in PWM mode, especially at higher output load
currents.
Low ESR capacitors such as X5R or X7R type ceramic
capacitors are recommended for input bypassing and
output fi ltering. Low-ESR tantalum capacitors are not rec-
Manufacturer/
Part #
Murata
LQH43MN4R7K03L
OUT
, (4.0V to 5.0V), and relatively high V
OUT
to reduce ripple in PSAVE mode and to ensure
Value
IN
(μH)
4.7
(0.7V to 0.8V) such as is obtained with a
DCR
(Ω)
0.4
Current
Rated
(mA)
500
Tolerance
(%)
10
IN
4.5 x 3.2 x 2.6
Dimensions
(3.3V and
LxWxH
(mm)
IN
ommended due to possible reduction in capacitance seen
at the switching frequency of the SC120. Ceramic capaci-
tors of type Y5V are not recommended as their tempera-
ture coeffi cients make them unsuitable for this application.
The following table lists recommended capacitors.
PCB Layout Considerations
Poor layout can degrade the performance of the DC-DC
converter and can contribute to EMI problems, ground
bounce, and resistive voltage losses. Poor regulation and
instability can result.
The following simple design rules can be implemented to
ensure good layout:
A layout drawing for the MLP package is shown in Figure 4
and a layout drawing for the SOT23 package is shown in
Figure 5.
Manufacturer/
Part Number
Murata
GRM21BR60J226ME39B
Murata
GRM31CR71A226KE15L
•
•
•
•
Place the inductor and fi lter capacitors as close
to the device as possible and use short wide
traces between the power components.
Route the output voltage feedback path away
from the inductor and LX node to minimize
noise and magnetic interference.
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.
Value
(μF)
22
22
Rated Voltage
(VDC)
6.3
10
Type
X5R
X7R
SC120
Case
0805
1206
Size
26