SC284P datasheet(20/22 Pages) SEMTECH

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SC284P

Figure 8 — PCB Bottom Layer

Applications Information (continued)

PCB Layout Considerations

The layout diagram in Figure 7 shows a recommended

PCB top layer for the SC284P and supporting components.

Figure 8 shows the bottom layer for this PCB. Fundamental

layout rules must be followed since the layout is critical for

achieving the performance specified in the Electrical

Characteristics table. Poor layout can degrade the perfor-

mance of the DC-DC converter and can contribute to EMI

problems, ground bounce, and resistive voltage losses.

Poor regulation and instability can result.

The following guidelines are recommended when devel-

oping a PCB layout:

The input capacitor, C

IN, should be placed as close

to the VIN and PGND pins as possible. This capacitor

provides a low impedance loop for the pulsed currents

present at the buck converter’s input. Use short wide

traces to connect as closely to the IC as possible.

This will minimize EMI and input voltage ripple by

localizing the high frequency current pulses.

Keep the LX pin traces as short as possible to minimize

pickup of high frequency switching edges to other

parts of the circuit. C

OUT and L should be connected as

close as possible between the LX and PGND pins, with

a direct return to the PGND pin from C

OUT.

Route the output voltage feedback/sense path away

from the inductor and LX node to minimize noise and

magnetic interference.

Use a ground plane referenced to the SC284P PGND

pin. Use several vias to connect to the component

side ground to further reduce noise and interference

on sensitive circuit nodes.

If possible, minimize the resistance from the output

and PGND pin to the load. This will reduce the voltage

drop on the ground plane and improve the load

regulation. It will also improve the overall efficiency

by reducing the copper losses on the output and

ground planes.

Connect the AGND pins to the thermal pad.

Figure 7 — Recommended PCB Layout (Top Layer)

Figure 9 — Recommended PCB Layout

(Top Layer Details)

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