SC643 datasheet(16/26 Pages) SEMTECH

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SC643

Applications Information (continued)

PCB Layout Considerations

The layout diagram in Figure 2 illustrates a proper two-

layer PCB layout for the SC643 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:

Place all bypass and decoupling capacitors —

C1, C2, CIN, COUT, CLDO1, 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.

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 — CLDO1, 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.

•

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:

PGND — CIN, COUT

AGND — Ground Pad, CLDO1, CLDO2,

CLDO3, CLDO4, CBYP

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.

•

Figure 2 — Recommended PCB Layout

Figure 3 — Layer 1

Figure 4 — Layer 2

COUT

BL2

BL1

LDO1

LDO2

BYP

LDO3

VIN

VOUT

SC643

BL3

PGND

CLDO1

AGND

PGND

SPIF

CLDO3

CLDO4

CLDO2

CBYP

CIN

PGND

Ground Plane

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