SC251 Datasheet, PDF (12/19 Pages) Semtech Corporation – Step-down DC-DC Converter with Bias LDO for WCDMA Amplifi ers

SC251
POWER MANAGEMENT
Applications Information (Cont.)
PCB Layout Considerations
Poor layout can degrade the performance of the DC-
DC converter and can be a contributory factor in 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:
1. Place the inductor and filter capacitors as close to the
device as possible and use short wide traces between
the power components.
2. Route the output voltage feedback and V_DAC path away
from the inductor and LX node to minimize noise and
magnetic interference.
3. Maximize ground metal on component side to improve
the return connection and thermal dissipation.
Separation between the LX node and GND should be
maintained to avoid coupling of switching noise to the
ground plane.
4. To further reduce noise interference on sensitive
circuit nodes, use a ground plane with several vias
connecting to the component side ground.
PGND
V_IN
VREF
GD
EN
C_REF
VMODE
VDAC
C_IN
LX
SC251
L_OUT
C_OUT
V_OUT
PGND
© 2006 Semtech Corp.
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