SC908 View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'SC908' PDF : 30 Pages View PDF
SC908
Applications Information (continued)
a few volts of bias. This is especially true of inexpensive
dielectrics. Insufficient SVOUT capacitance can cause
rapid decay of output voltage between PSAVE bursts,
resulting in poor low-load efficiency, PSAVE/PWM mode
cycling, and other erratic behaviors.
Switcher Grounding and PCB Layout Consider-
ations
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.
A few 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.
• 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 SLX node
and GND should be maintained to avoid cou-
pling of switching noise to 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.
Charger Grounding and PCB Layout Consider-
ations
While layout for linear devices is generally not as critical as
for a switching application, careful attention to detail will
ensure reliable operation.
• Attaching the part to a larger copper footprint
will enable better heat transfer from the device,
especially on PCBs with internal ground and
power planes.
• Place the input, output and bypass capacitors
close to the device for optimal transient response
and device behavior.
• Connect all ground connections directly to the
ground plane. If there is no ground plane,
connect to a common local ground point before
connecting to board ground.
• The DGND pin and PGND pin should be con-
nected directly to the PCB ground plane as close
to the part as possible. The thermal pad should
be connected to the ground plane with thermal
vias under the SC908.
• The nodes indicated as AGND in the Block
Diagram should be connected together and to
the AGND pin. The AGND pin should be tied to
the DGND pin at a single point close to the
SC908.
• Route the BSEN trace directly to the battery posi-
tive terminal connection on the PCB.
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