SC221 datasheet(11/14 Pages) SEMTECH

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SC221 x

Applications Information (Cont.)

PCB Layout Considerations

Fundamental layout rules must be followed since the

layout is critical for achieving the desirable performance.

Poor layout can degrade the performance of the DC-DC

converter and can contribute to EMI problems, ground

bounce, and resistive voltage losses, and possibly poor

regulation and instability.

The following guidelines are recommended when devel-

oping a PCB layout:

1. The input capacitor, C

IN 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.

2. Keep the SW 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 SW and GND pins, with

a direct return to the GND pin from C

OUT.

3. Route the output voltage feedback/sense path away

from the inductor and SW node to minimize noise

and magnetic interference to the output feedback/

sense path.

4. 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.

5. If possible, minimize the resistance from the VOUT

and AGND pin 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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