SC220 datasheet(11/14 Pages) SEMTECH

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SC220

Applications Information (Cont.)

PCB Layout Considerations

PCB Layout is important in designing a switching regula-

tor. A few fundamental layout considerations will help to

achieve the specified performance. Poor layout can

degrade the performance of the switching regulator and

may contribute to EMI problems, ground bounce, and

possibly poor regulation and instability.

The following guidelines are recommended when devel-

oping a PCB layout:

The input capacitor, C

should be placed as close to

the PVIN 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 this capacitor as close

to the IC as possible. This will minimize EMI and input

voltage ripple by localizing the high frequency current

pulses.

Keep the SW pin traces as short as possible to minimize

the pickup of high frequency switching edges to

other parts of the circuit. The output capacitor, C

OUT

and the inductor should be put as close as possible to

the related pins of the IC, and connected as close as

possible between the SW and ground pins.

Route the output voltage feedback/sense path

from the output capacitor path, and away from the

inductor and SW node to minimize the possible noise

and magnetic interference to the output feedback/

sense path.

Use a ground plane referenced to the PGND pin,

and the ground connection of the input and output

capacitors should be put on this plane and close to

each other if possible, and as close to the PGND pin as

possible. 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 VOUT

and AGND pins to the load. This will reduce the

voltage drop on the ground plane and improve the

load regulation. And it will also improve the overall

efficiency by reducing the copper losses on the output

and ground planes.

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