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參數(shù)資料
| 型號： | LM3691TLX-0.85 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1.7 A SWITCHING REGULATOR, 4400 kHz SWITCHING FREQ-MAX, PBGA6 |
| 封裝： | MICRO, SMD-6 |
| 文件頁數(shù)： | 9/20頁 |
| 文件大?。?/td> | 1921K |
| 代理商： | LM3691TLX-0.85 |
PRINTED CIRCUIT BOARD LAYOUT CONSIDERATIONS
PC board layout is an important part of DC-DC converter de-
sign. 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, re-
sulting in poor regulation or instability. In particular parasitic
inductance from extra-long PCB trace lengths can cause ad-
ditional noise voltages through L*di/dt that adversely affect
the DC-DC converter IC circuitry. Good layout for the LM3691
can be implemented by following a few simple design rules.
1.
Place the inductor and filter capacitors close together
and make the traces short. The traces between these
components carry relatively high switching currents and
act as antennas. Following this rule reduces radiated
noise.
2.
Place the capacitors and inductor close to the LM3691.
Place the C
IN capacitor as close as possible to the VIN
and GND pads. Place the C
OUT capacitor as close as
possible to the VOUT and GND connections.
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 buck 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 buck 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 magnetic
field reversal between the two half-cycles and reduces
radiated noise.
4.
Connect the ground pins of the buck and filter capacitors
together using generous component-side copper fill as a
pseudo-ground plane. 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 buck 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 by resistive losses across the
traces. Even 1mm of fine trace creates parasitic
inductance that can undesirably affect performance from
increased L*di/dt noise voltages.
6.
Route noise sensitive traces, such as the voltage
feedback path, away from noisy traces between the
power components. The voltage feedback trace must
remain close to the buck circuit and should be routed
directly from FB to VOUT at the output capacitor and
should be routed opposite to noise components. This
reduces EMI radiated onto the DC-DC converter’s own
voltage feedback trace.
MICRO SMD PACKAGE ASSEMBLY AND USE
Use of the micro SMD package requires specialized board
layout, precision mounting and careful re-flow techniques, as
detailed in National Semiconductor Application Note 1112.
Refer to the section Surface Mount Technology (SMD) As-
sembly Considerations. For best results in assembly, align-
ment ordinals on the PC board should be used to facilitate
placement of the device. 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. This prevents a lip that otherwise forms if the solder-
mask and pad overlap, from holding the device off the surface
of the board and interfering with mounting. See Application
Note 1112 for specific instructions how to do this.
The 6-bump package used for LM3691 has 300-micron solder
balls and requires 10.82 mils 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 cor-
ners. Initially, the trace to each pad should be 7 mil wide, for
a section approximately 7 mil long or longer, as a thermal re-
lief. Then each trace should neck up or down to its optimal
width. The important criteria is symmetry. This ensures the
solder bumps on the LM3691 re-flow evenly and that the de-
vice solders level to the board. In particular, special attention
must be paid to the pads for bumps A2 and C2, because GND
and V
IN are typically connected to large copper planes.
The micro SMD package is optimized for the smallest possi-
ble size in applications with red or infrared opaque cases.
Because the micro SMD package lacks the plastic encapsu-
lation characteristic of larger devices, it is vulnerable to light.
Backside metallization and/or epoxy coating, along with front
side shading by the printed circuit board, reduce this sensi-
tivity. However, the package has exposed die edges. In par-
ticular, micro SMD devices are sensitive to light, in the red
and infrared range, shining on the package’s exposed die
edges.
17
www.national.com
LM3691
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參數(shù)描述 |
|---|---|
| LM3691TLX-09 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Accuracy, Miniature 1A, Step-Down DC-DC Converter for Portable Applications |
| LM3691TLX-1.0 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Accuracy, Miniature 1A, Step-Down DC-DC Converter for Portable Applications |
| LM3691TLX-1.0/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Hi Acc Mini 1A SD DC-DC Cnvtr RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM3691TLX-1.1 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Accuracy, Miniature 1A, Step-Down DC-DC Converter for Portable Applications |
| LM3691TLX-1.2 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Accuracy, Miniature 1A, Step-Down DC-DC Converter for Portable Applications |
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