SC3303 datasheet(23/26 Pages) SEMTECH

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SC3303

Applications Information (continued)

to AGND are done by wide copper traces or vias

down to AGND.

Connect PGND to AGND with a short trace or 0Ω

resistor. This connection should be as close to

the IC as possible.

FB and Other Analog Control Signals

The connection from the V

OUT

power to the

analog control circuitry must be routed from the

output capacitors and located on a quiet layer.

The traces between V

OUT

and the analog control

circuitry (AGND, and FB pins) must be as short as

possible. The traces must also be routed away

from noise sources, such as BST, LX, VIN, and

PGND between the input capacitors, output

capacitors, and the IC.

The TON node must be as short as possible to

ensure the best accuracy for the on time.

The feedback components for the switcher need

to be as close to the FB pin of the IC as possible

to reduce the possibility of noise corrupting

these analog signals.

•

BST and LX

LX and BST are very noisy nodes and must be

carefully routed to minimized the PCB area that

is exposed to these signals.

The connections for

the boost capacitor

between the IC and LX must be short and directly

connected to the LX (pin 3).

The LX node between the IC and the inductor

should be wide enough to handle the inductor

current and short enough to eliminate the pos-

sibility of LX noise corrupting other signals.

Capacitors and Current Loops

The current loops between the input capacitors,

the IC, the inductor, and the output capacitors

must be as close as possible to each other to

reduce IR drop across copper planes and traces.

All bypass and output capacitors must be con-

nected as close as possible to their respective

pin on the IC.

•

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