LM26 datasheet(17/19 Pages) NSC

17 / 19 page

Application Information (Continued)

Place the LM2612 on 10.82mil pads for micro SMD

package. As a thermal relief, connect to each pad with a

6mil wide trace (micro SMD), 6mils long or longer, then

incrementally increase each trace to its optimal width

over a span so that the taper extends beyond the edge

of the package. The important criterion is symmetry, to

ensure re-flow occurs evenly (see Micro SMD Package

Assembly and Use).

Place the LM2612, inductor and filter capacitors close

together and make the traces short. The traces between

these components carry relatively high switching cur-

rents and act as antennas. Following this rule reduces

radiated noise. Place the capacitors and inductor within

0.2in (5mm) of the LM2612.

Arrange the components so that the switching current

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

each cycle, current flows from the input filter capacitor,

through the LM2612 and inductor to the output filter

capacitor and back through ground, forming a current

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

up from ground, through the LM2612 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 part-cycles and

reduces radiated noise.

Connect the ground pins of the LM2612 and filter ca-

pacitors together using generous component-side cop-

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

the ground-plane with several vias. This reduces

ground-plane noise by preventing the switching currents

from circulating through the ground plane. It is recom-

mended to have a dedicate ground plan between the

switch signal and feedback traces. It also reduces

ground bounce at the LM2612 by giving it a low-

impedance ground connection.

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.

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 LM2612 circuit and should be direct but

routed away from noisy components. This reduces EMI

radiated onto the DC-DC converter’s own voltage feed-

back trace.

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 in 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 in the diagonally opposing corner. Often, the sen-

sitive circuitry is shielded with a metal pan and power to it is

post-regulated to reduce conducted noise, using low-dropout

linear regulators, such as the LP2966.

LM26 датащи(PDF) 17 Page - National Semiconductor (TI)

LM26 датащи(HTML) 17 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

датащи скачать

ссылки URL