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参数资料
| 型号： | LX1681CDM-TR |
| 厂商： | MICROSEMI CORP-ANALOG MIXED SIGNAL GROUP |
| 元件分类： | 稳压器 |
| 英文描述： | 1 A SWITCHING CONTROLLER, 230 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封装： | ROHS COMPLIANT, PLASTIC, SOIC-8 |
| 文件页数： | 7/9页 |
| 文件大小： | 199K |
| 代理商： | LX1681CDM-TR |
Microsemi
Linfinity Microelectronics Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
Copyright
2000
Rev. 1.1b,2005-03-09
WWW
.Microse
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.CO
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LX1681/1682
Voltage-Mode PWM Controllers
PRODUCTION DATA SHEET
TM
APPLI CATI ON I N FORMATI O N
FET SELECTION (continued)
Synchronous Rectification – Lower MOSFET
The lower pass element can be either a MOSFET or a Schottky
diode. The use of a MOSFET (synchronous rectification) will
result in higher efficiency, but at higher cost than using a Schottky
diode (non-synchronous). Power dissipated in the bottom
MOSFET will be:
[]
W
Cycle
Duty
R
I
P
ON
DS
D
51
.
3
1
)
(
2
=
×
=
[IRL3303 or 1.76W for the IRL3102]
Non-Synchronous Operation - Schottky Diode
A typical Schottky diode, with a forward drop of 0.6V will
dissipate 0.6 * 15 * [1 – 2/5] = 5.4W (compared to the 1.8 to 3.5W
dissipated by a MOSFET under the same conditions). This power
loss becomes much more significant at lower duty cycles. The use
of a dual Schottky diode in a single TO-220 package (e.g. the
MBR2535) helps improve thermal dissipation.
Operation From A Single Power Supply
The LX1681/1682 needs a secondary supply voltage (VC1) to
provide sufficient drive to the upper MOSFET. In many
applications with a 5V (VCC) and a 12V (VC1) supply are present.
In situations where only 5V is present, VC1 can be generated using
a bootstrap (charge pump) circuit, as shown in Figure 4 (Typical
Applications section). The capacitor (C4) is alternatively charged
up from VCC via the Schottky diode (D2), and then boosted up
when the FET is turned on. This scheme provides a VC1 voltage
equal to 2 * VCC - VDS (D2), or approximately 9.5V with VCC = 5V.
This voltage will provide sufficient gate drive to the external
MOSFET in order to get a low RDS(ON) . Note that using the
bootstrap circuit in synchronous rectification mode is likely to
result in faster turn-on than in non-synchronous mode.
LAYOUT GUIDELINES - THERMAL DESIGN
A great deal of time and effort were spent optimizing the
thermal design of the demonstration boards. Any user who intends
to implement an embedded motherboard would be well advised to
carefully read and follow these guidelines. If the FET switches
have been carefully selected, external heatsinking is generally not
required. However, this means that copper trace on the PC board
must now be used. This is a potential trouble spot; as much copper
area as possible must be dedicated to heatsinking the FET
switches, and the diode as well if a non-synchronous solution is
used. In our VRM module, heatsink area was taken from internal
ground and VCC planes which were actually split and connected
with VIAS to the power device tabs. The TO-220 and TO-263
cases are well suited for this application, and are the preferred
packages. Remember to remove any conformal coating from all
exposed PC traces which are involved in heatsinking.
LX168x
5V Input
O utput
GND
FIGURE 2 — Enabling Linear Regulator
General Notes
As always, be sure to provide local capacitive decoupling close
to the chip. Be sure use ground plane construction for all high-
frequency work. Use low ESR capacitors where justified, but be
alert for damping and ringing problems. High-frequency designs
demand careful routing and layout, and may require several
iterations to achieve desired performance levels.
Power Traces
To reduce power losses due to ohmic resistance, careful consid-
eration should be given to the layout of traces that carry high
currents. The main paths to consider are:
Input power from 5V supply to drain of top MOSFET.
Trace between top MOSFET and lower MOSFET or
Schottky diode.
Trace between lower MOSFET or Schottky diode and
ground.
Trace between source of top MOSFET and inductor and
load.
All of these traces should be made as wide and thick as possible,
in order to minimize resistance and hence power losses. It is also
recommended that, whenever possible, the ground, input and
output power signals should be on separate planes (PCB layers).
See Figure 2 – bold traces are power traces.
Layout Assistance
Please contact Linfinity’s Applications Engineers for assistance
with any layout or component selection issues. A Gerber file with
layout for the most popular devices is available upon request.
Evaluation boards are also available upon request. Please check
Linfinity's web site for further application notes.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LX1681IDM | 功能描述:IC REG CTRLR DIVIDER PWM 8-SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,000 系列:- PWM 型:电压模式 输出数:1 频率 - 最大:1.5MHz 占空比:66.7% 电源电压:4.75 V ~ 5.25 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 85°C 封装/外壳:40-VFQFN 裸露焊盘 包装:带卷 (TR) |
| LX1682 | 制造商:MICROSEMI 制造商全称:Microsemi Corporation 功能描述:VOLTAGE - MODE PWM CONTROLLERS |
| LX1682CDM | 功能描述:IC REG CTRLR DIVIDER PWM 8-SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,000 系列:- PWM 型:电压模式 输出数:1 频率 - 最大:1.5MHz 占空比:66.7% 电源电压:4.75 V ~ 5.25 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 85°C 封装/外壳:40-VFQFN 裸露焊盘 包装:带卷 (TR) |
| LX1682CDMT | 制造商:MICROSEMI 制造商全称:Microsemi Corporation 功能描述:Voltage-Mode SMPS Controller |
| LX1682CDM-TR | 制造商:MICROSEMI 制造商全称:Microsemi Corporation 功能描述:Voltage-Mode PWM Controllers |
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