SC284 datasheet(18/20 Pages) SEMTECH

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SC284

PCB Layout Considerations

The layout diagram in Figure 7 shows a recommended

top-layer PCB for the SC284 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

performance 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

developing a PCB layout:

Theinputcapacitor,C

IN, should be placed as close to the

VIN and GND 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 GND pins, with

a direct return to the GND 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 SC284 GND 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 GND 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.

Figure 7 — Recommended PCB Layout (Top Layer)

Figure 8 — Bottom Layer Detail

Applications Information (continued)

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