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| 型号： | LM3686TLE-AAEF/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 20/27页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC .9A TRPL 12USMD |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 3 |
| 输出电压： | 1.2V，1.8V，2.8V |
| 输入电压： | 2.7 V ~ 5.5 V |
| PWM 型： | 电流/电压模式 |
| 频率 - 开关： | 3MHz |
| 电流 - 输出： | 900mA |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 12-WFBGA |
| 包装： | 标准包装 |
| 供应商设备封装： | 12-uSMD |
| 产品目录页面： | 1288 (CN2011-ZH PDF) |
| 其它名称： | LM3686TLE-AAEFDKR |
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SNVS520E – AUGUST 2008 – REVISED MAY 2013
surface of the board and interfering with mounting. See TI AN-1112 Application Report ( SNVA009 ) for specific
instructions how to do this. The 12-bump package used for LM3686 has 300 micron solder balls and requires
275 micron 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 not exceed 183
micron, for a section approximately 183 micron long or longer, as a thermal relief. Then each trace should neck
up or down to its optimal width. The important criteria is symmetry. This ensures the solder bumps on the
LM3686 re-flow evenly and that the device solders level to the board. In particular, special attention must be paid
to the pads for bumps A1, A2, C1 and B3, because PGND, SGND, V BATT and V IN_LIN are typically connected to
large copper planes, inadequate thermal relief can result in late or inadequate re-flow of these bumps. The
DSBGA package is optimized for the smallest possible size in applications with red or infrared opaque cases.
Because the DSBGA package lacks the plastic encapsulation characteristic of larger devices, it is vulnerable to
light. Backside metallization and/or epoxy coating, along with frontside shading by the printed circuit board,
reduce this sensitivity. However, the package has exposed die edges. In particular, DSBGA devices are sensitive
to light, in the red and infrared range, shining on the package’s exposed die edges.
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. Good layout for the LM3686 can be implemented by following a few simple design rules below.
1. Place the LM3686, inductor and filter capacitor 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. Special care must be given to place the input filter capacitor very close to the V BATT
and PGND pin. Place the output capacitor of the linear regulator close to the output pin.
2. 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 LM3686 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 LM3686 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.
3. Connect the ground pins of the LM3686 and filter capacitors together using generous component-side
copper 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 LM3686 by giving it a low impedance ground connection.
Route SGND to the ground-plane by a separate trace.
4. 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.
5. Route noise sensitive traces, such as the voltage feedback path (FB_DCDC), away from noisy traces
between the power components. The voltage feedback trace must remain close to the LM3686 circuit and
should be direct but should be routed opposite to noisy components. This reduces EMI radiated onto the DC-
DC converter’s own voltage feedback trace. A good approach is to route the feedback trace on another layer
and to have a ground plane between the top layer and layer on which the feedback trace is routed.
6. 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 plane; power to it is post-regulated to reduce conducted noise, a good field of application for the on-chip
low-dropout linear regulator.
20
Product Folder Links: LM3686
Copyright ? 2008–2013, Texas Instruments Incorporated
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM3686TLX-AADW | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Step-Down DC-DC Converter with Integrated Post Linear Regulators System and Low-Noise Linear Regulator |
| LM3686TLX-AADW/NOPB | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM3686TLX-AAED | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Step-Down DC-DC Converter with Integrated Post Linear Regulators System and Low-Noise Linear Regulator |
| LM3686TLX-AAED/NOPB | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM3686TLX-AAEF | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Step-Down DC-DC Converter with Integrated Post Linear Regulators System and Low-Noise Linear Regulator |
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