參數(shù)資料
型號(hào)： LM261J
英文描述： Analog Comparator
中文描述： 模擬比較器
文件頁(yè)數(shù)： 17/19頁(yè)
文件大?。?/td> 2317K
代理商： LM261J
Application Information
(Continued)
1.
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
2.
3.
4.
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
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.
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.
LM2612
by
giving
it
a
5.
6.
7.
Interference
with
L
www.national.com
17
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