Specifications

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Application Information (Continued)

3. Arrange the components so that the switching current

loops curl in the same direction. During the first half of

each cycle, current flows from the input filter capacitor,

through the LM2614 and inductor to the output filter

capacitor and back through ground, forming a current

loop. In the second half of each cycle, current is pulled

up from ground, through the LM2614 by the inductor, to

the output filter capacitor and then back through ground,

forming a second current loop. Routing these loops so

the current curls in the same direction prevents mag-

netic field reversal between the two half-cycles and re-

duces radiated noise.

4. Connect the ground pins of the LM2614, and filter ca-

pacitors together using generous component-side cop-

per fill as a pseudo-ground plane. Then, connect this to

the ground-plane (if one is used) with several vias. This

reduces ground-plane noise by preventing the switching

currents from circulating through the ground plane. It

also reduces ground bounce at the LM2614 by giving it

a low-impedance ground connection.

5. Use wide traces between the power components and for

power connections to the DC-DC converter circuit. This

reduces voltage errors caused by resistive losses across

the traces.

6. Route noise sensitive traces, such as the voltage feed-

back path, away from noisy traces between the power

components. The voltage feedback trace must remain

close to the LM2614 circuit and should be routed directly

from V

OUT

at the output capacitor and should be routed

opposite to noise components. This reduces EMI radi-

ated onto the DC-DC converter’s own voltage feedback

trace.

7. Place noise sensitive circuitry, such as radio IF blocks,

away from the DC-DC converter, CMOS digital blocks

and other noisy circuitry. Interference with

noise-sensitive circuitry in the system can be reduced

through distance.

In mobile phones, for example, a common practice is to

place the DC-DC converter on one corner of the board,

arrange the CMOS digital circuitry around it (since this also

generates noise), and then place sensitive preamplifiers and

IF stages on the diagonally opposing corner. Often, the

sensitive circuitry is shielded with a metal pan and power to

it is post-regulated to reduce conducted noise, using

low-dropout linear regulators.

LM2614