SC644 SEMTECH [Semtech Corporation], SC644 Datasheet - Page 16

• Manufacturer Part Number: SC644
• Manufacturer: SEMTECH [Semtech Corporation]

Applications Information (continued)
PCB Layout Considerations
The layout diagram in Figure 2 illustrates a proper two-
layer PCB layout for the SC644 and supporting
components. Following fundamental layout rules is
critical for achieving the performance specified in the
Electrical Characteristics table. The following guidelines
are recommended when developing a PCB layout:
PGND
Ground Plane
•
•
•
•
VIN
CIN
Ensure that all connections to these pins make
use of wide traces so that the resistive drop on
each connection is minimized.
The thermal pad should be connected to the
ground plane using multiple vias to ensure
proper thermal connection for optimal heat
transfer.
The following capacitors — CLDO, CLDO2,
CLDO3, CLDO4, and CBYP should be grounded
together. Connect these capacitors to the
ground plane at one point near the AGND pin
as shown in Figure 2.
Place all bypass and decoupling capacitors —
C, C2, CIN, COUT, CLDO, CLDO2, CLDO3,
CLDO4, and CBYP as close to the device as
possible.
All charge pump current passes through IN,
OUT, and the bucket capacitor connection pins.
Figure 2 — Recommended PCB Layout
PGND
IN
BL3
BL2
BL1
SC644
PGND
C2
C1
LDO2
LDO1
LDO3
VOUT
BYP
SPIF
AGND
COUT
CLDO1
CLDO2
CLDO3
CLDO4
CBYP
PGND
•
•
•
•
Figure 3 shows the pads that should be con-
nected to the ground plane with multiple vias.
Make all ground connections to a solid ground
plane as shown in Figure 4.
If a ground layer is not feasible, the following
groupings should be connected:


If no ground plane is available, PGND and AGND
should be routed back to the negative battery
terminal, separately, using thick traces. Joining
the two ground returns at the terminal prevents
large pulsed return currents from mixing with
the low-noise return currents of the LDOs.
All LDO output traces should be made as wide
as possible to minimize resistive losses.
PGND — CIN, COUT
AGND — Ground Pad, CLDO, CLDO2,
CLDO3, CLDO4, CBYP
Figure 3 — Layer 1
Figure 4 — Layer 2
SC644
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