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參數(shù)資料
| 型號： | LM2608ATL-1.8 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 400mA Sub-miniature, High Efficiency, Programmable DC-DC Converter with Linear Mode |
| 中文描述： | 0.69 A SWITCHING REGULATOR, 690 kHz SWITCHING FREQ-MAX, PBGA10 |
| 封裝： | MICRO, SMD-10 |
| 文件頁數(shù)： | 17/18頁 |
| 文件大小： | 728K |
| 代理商： | LM2608ATL-1.8 |
Application Information
(Continued)
MICRO SMD PACKAGE ASSEMBLY AND USE
Use of the Micro SMD package requires specialized board
layout, precision mounting and careful reflow techniques, as
detailed in National Semiconductor Application Note AN-
1112. Refer to the section
Surface Mount Technology (SMT)
Assembly Considerations
. For best results in assembly,
alignment ordinals on the PC board should be used to
facilitate placement of the device. Since Micro SMD packag-
ing is a new technology, all layouts and assembly means
must be thoroughly tested prior to production. In particular,
proper placement, solder reflow and resistance to thermal
cycling must be verified.
The 10-Bump package used for the LM2608 has 300micron
solder balls and requires 10.82mil (0.275mm) pads for
mounting on the circuit board. The trace to each pad should
enter the pad with a 90 entry angle to prevent debris from
being caught in deep corners. Initially, the trace to each pad
should be 6 mil wide, for a section 6 mil long or longer, as a
thermal relief. Then each trace should neck up to its optimal
width over a span of 11 mils or more, so that the taper
extends beyond the edge of the package. The important
criterion is symmetry. This ensures the solder bumps on the
LM2608 re-flow evenly and that the device solders level to
the board. In particular, special attention must be paid to the
pads for bumps D3, C3, B3, A3 and A2. Because PVIN and
PGND are typically connected to large copper planes, inad-
equate thermal reliefs can result in late or inadequate reflow
of these bumps.
The pad style used with Micro SMD package must be the
NSMD (non-solder mask defined) type. This means that the
solder-mask opening is larger than the pad size or 14.7mils
for the LM2608. This prevents a lip that otherwise forms if
the solder-mask and pad overlap. This lip can hold the
device off the surface of the board and interfere with mount-
ing. See Applications Note AN-1112 for specific instructions.
BOARD LAYOUT CONSIDERATIONS
PC board layout is an important part of DC-DC converter
design. Poor board layout can disrupt the performance of a
DC-DC converter and surrounding circuitry by contributing to
EMI, ground bounce, and resistive voltage loss in the traces.
These can send erroneous signals to the DC-DC converter
IC, resulting in poor regulation or instability. Poor layout can
also result in reflow problems leading to poor solder joints
between the Micro SMD package and board pads. Poor
solder joints can result in erratic or degraded performance.
Good layout for the LM2608 can be implemented by follow-
ing a few simple design rules:
1.
Place the LM2608 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 LM2608, 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 LM2608.
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 LM2608 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 LM2608 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 LM2608 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 LM2608 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 LM2608 circuit and should be routed away
from noisy components. This reduces EMI radiated onto
the DC-DC converter’s own voltage feedback 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 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, such as the LP2966.
2.
3.
4.
5.
6.
7.
L
www.national.com
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2608ATLX-1.3 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:400mA Sub-miniature, High Efficiency, Programmable DC-DC Converter with Linear Mode |
| LM2608ATLX-1.8 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:400mA Sub-miniature, High Efficiency, Programmable DC-DC Converter with Linear Mode |
| LM2608ATLX-1.8/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| LM260H | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Analog Comparator |
| LM260P | 制造商:DYMO 功能描述:Bulk |
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