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參數(shù)資料
| 型號： | LM1946M |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 電源管理 |
| 英文描述： | LM1946 Over/Under Current Limit Diagnostic Circuit |
| 中文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO20 |
| 封裝： | 0.300 INCH, PLASTIC, SOP-20 |
| 文件頁數(shù)： | 10/12頁 |
| 文件大小： | 216K |
| 代理商： | LM1946M |
Application Hints
(Continued)
MORE NOISE FILTERING
The current flowing through the sense resistor and certain
loads can sometimes be very noisy, particularly when the
load is a DC motor, or switching supply. Large amounts of
noise on the supply line can also cause problems when
threshold voltages are set to very small values. In these
cases, while the average current level may remain well be-
low the threshold trip point, noise peaks may exceed it. A
LED display could then flicker or appear dimly lit, or exces-
sive software routines and processor time may be required
for a
m
P to disregard such noise. Often such noise must be
filtered directly at the inputs, using the input resistors R1
and R2 and a capacitor. Care must be taken, however, that
such a filter will not cause an erroneous output state upon
power-up or whenever switch S1 is closed. The most effec-
tive general methodology to achieve this is to split the resis-
tor in the positive input lead into two resistor values and
connect a capacitor from here to the negative input. For
example, the 1.2k resistor R2 of Figure 10 could be re-
placed with 3.9k and 1.2k resistors as shown in Figure 16a
(R1 increasing from 6.2k to 10k to compensate). The value
of capacitor C2 depends upon the degree of filtering re-
quired, the amount of noise present, and the response times
desired. The choice of values for the new resistors is almost
arbitrary. Generally the larger value is attached to the sense
resistor for better decoupling. The smaller value must be
large enough so that the DC voltage across it upon power-
up exceeds the maximum offset voltage expected of the
comparator (i.e. Iset
*
R2b
l
5.0mV). It is this requirement
that guarantees that the output will not be in an erroneous
high state upon power-up or whenever S1 is closed. (Should
this feature be unnecessary to a particular application cir-
cuit, the methodology described can be replaced with a sim-
ple capacitor across the comparator input pins).
For extremely severe cases, additional filter stages can be
cascaded at the inputs (seeFigure 17). Since the input bias
currents of the comparator are equal at the input threshold
level, the voltage drops across the 1k resistors cancel and
do not affect the DC operation of the circuit (ignoring resis-
tor match tolerance and Ios). If an application circuit is noisy
enough to require such an elaborate filter, then ferrite
beads, shown here as L1 and L2, will also probably help.
TL/H/8707–16
a. Open-Circuit Detector
TL/H/8707–17
b. Over-Current Limit Detector
FIGURE 16. Input Noise Filters for
Various Application Circuits
TL/H/8707–18
FIGURE 17. Additional Noise Filters
10
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| LM1946N | LM1946 Over/Under Current Limit Diagnostic Circuit |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM1946N | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:LM1946 Over/Under Current Limit Diagnostic Circuit |
| LM1949 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:LM1949 Injector Drive Controller |
| LM1949M | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:LM1949 Injector Drive Controller |
| LM1949N | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| LM1949N/NOPB | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
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