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参数资料
| 型号： | LM3420A-8.4MWA |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 电源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, UUC |
| 封装： | WAFER |
| 文件页数： | 4/21页 |
| 文件大小： | 468K |
| 代理商： | LM3420A-8.4MWA |
V
REG External Voltage Trim (Continued)
R
increase = 26x10
5/%incr
R
decrease = (150x10
5/%decr) 176x103
For LM3420-8.4
R
increase = 26x10
5/%incr
R
decrease = (154x10
5/%decr) 181x103
For LM3420-12.6
R
increase = 28x10
5/%incr
R
decrease = (259x10
5/%decr) 287x103
For LM3420-16.8
R
increase = 29x10
5/%incr
R
decrease = (364x10
5/%decr) 392x103
Application Information
The LM3420 regulator/driver provides the reference and
feedback drive functions for a Lithium-Ion battery charger. It
can be used in many different charger configurations using
both linear and switching topologies to provide the precision
needed for charging Lithium-Ion batteries safely and effi-
ciently. Output voltage tolerances better than 0.5% are pos-
sible without using trim pots or precision resistors. The cir-
cuits shown are designed for 2 cell operation, but they can
readily be changed for either 1, 3 or 4 cell charging applica-
tions.
One item to keep in mind when designing with the LM3420 is
that there are parasitic diodes present. In some designs, un-
der special electrical conditions, unwanted currents may
flow. Parasitic diodes exist from OUT to IN, as well as from
GROUND to IN. In both instances the diode arrow is pointed
toward the IN pin.
Application Circuits
The circuit shown in
Figure 5 performs constant-current,
constant-voltage charging of two Li-Ion cells. At the begin-
ning of the charge cycle, when the battery voltage is less
than 8.4V, the LM3420 sources no current from the OUT pin,
keeping Q2 off, thus allowing the LM317 Adjustable voltage
regulator to operate as a constant-current source. (The
LM317 is rated for currents up to 1.5A, and the LM350 and
LM338 can be used for higher currents.) The LM317 forces
a constant 1.25V across R
LIM, thus generating a constant
current of
I
LIM = 1.25V/RLIM
Transistor Q1 provides a disconnect between the battery
and the LM3420 when the input voltage is removed. This
prevents the 85 A quiescent current of the LM3420 from
eventually discharging the battery. In this application Q1 is
used as a low offset saturated switch, with the majority of the
base drive current flowing through the collector and crossing
over to the emitter as the battery becomes fully charged. It
provides a very low collector to emitter saturation voltage
(approximately 5 mV). Diode D1 is also used to prevent the
battery current from flowing through the LM317 regulator
from the output to the input when the DC input voltage is re-
moved.
As the battery charges, its voltage begins to rise, and is
sensed at the IN pin of the LM3420. Once the battery voltage
reaches 8.4V, the LM3420 begins to regulate and starts
sourcing current to the base of Q2. Transistor Q2 begins
DS012359-1
FIGURE 5. Constant Current/Constant Voltage Li-Ion Battery Charger
DS012359-11
FIGURE 6. Low Drop-Out Constant Current/Constant Voltage 2-Cell Charger
LM3420-4.2/LM3420-8.2/LM3420-8.4/LM3420-12.6/LM3420-16.8
www.national.com
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM3420AL-4.2 DIE | 制造商:Texas Instruments 功能描述: |
| LM3420AL-8.2 WAF | 制造商:Texas Instruments 功能描述: |
| LM3420AM5-12.6 | 功能描述:IC CTRLR LIION BAT CHRG SOT23-5 RoHS:否 类别:集成电路 (IC) >> PMIC - 电池管理 系列:- 标准包装:1 系列:- 功能:充电管理 电池化学:锂离子（Li-Ion）、锂聚合物（Li-Pol） 电源电压:3.75 V ~ 6 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SC-74A，SOT-753 供应商设备封装:SOT-23-5 包装:剪切带 (CT) 产品目录页面:669 (CN2011-ZH PDF) 其它名称:MCP73831T-2ACI/OTCT |
| LM3420AM5-12.6/NOPB | 制造商:Texas Instruments 功能描述:Battery Charger Li-Ion 15mA 12.6V 5-Pin SOT-23 T/R |
| LM3420AM5-16.8 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Lithium-Ion Battery Charge Controller |
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