- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄385476 > LM1946M (NATIONAL SEMICONDUCTOR CORP) LM1946 Over/Under Current Limit Diagnostic Circuit PDF資料下載
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)： | 8/12頁 |
| 文件大?。?/td> | 216K |
| 代理商： | LM1946M |
Application Hints
(Continued)
TL/H/8707–7
FIGURE 10. Using the LM1946 as an Over-Current Limit Detector
and R4 again allow the system designer to tailor the thresh-
old limit to the V/I characteristics of each particular system.
The input threshold voltage is determined by, and directly
proportional to, Iset into pin 20. R3, from the on-chip refer-
ence voltage, provides a current and threshold that is inde-
pendent of the supply voltage, V
CC
. R4 provides a current
directly proportional to supply. These resistors allow thresh-
olds to be either independent of, or directly proportional to
supply voltage, or anything in between. For example, the
values inFigure 10 are tailored to match the V/I characteris-
tics of the bulb filament used in earlier examples. However,
if the load had purely resistive characteristics, Iset and the
threshold would be set with R4 only, eliminating R3. Like-
wise, if the load current was independent of supply, such as
in many systems powered by a voltage regulator, Iset would
be better set by R3 only, eliminating R4. Further details on
this and how to handle variations with ambient temperature
with resistor and thermistor combinations are discussed in
detail in previous sections. Compensation for temperature
variations, however, is rarely necessary since short circuit or
over-current values are usually much greater than the nomi-
nal value. For example, if the load inFigure 10 represented
a DC motor, the circuit could be used to detect the motor
stall condition. Stall current through the sense resistor, Rs,
would typically be five times the nominal running current. By
setting the threshold at three times the nominal current val-
ue, enough margin exists that minor variations due to tem-
perature can be ignored. The variation in stall current due to
battery or supply voltage can be significant, however. Being
approximately proportional, Iset would best be set in this
case by R4 only.
WINDOW DETECTOR
The availability of more than one comparator per IC allows
many other applications. One is the current sense window
detector. Many times it is useful to know that a certain cur-
rent is within both an upper and lower limit. Using two of the
LM1946 comparators and the circuit of Figure 11 will ac-
complish this. In this particular case, high and low limits
are approximately 3A and 1A respectively. The outputs can
be kept separate or wired-or, as shown, to a single output
load as a simple out-of-bounds detector.
Vthrshld-lo
e
Iset
#
(R10
b
R11)
Vthrshld-hi
e
Iset
#
(R13
b
R12)
TL/H/8707–8
FIGURE 11. Current Limit Window Detector
COMPARATOR INPUT STAGE
The LM1946 IC consists of five specially designed compara-
tor input circuits to monitor the IR drop across the wiring
harness or the sense resistor between the battery and the
light bulb. These comparators have been designed to ac-
commodate a wide range of input signals without damage to
the IC or the load circuitry. The inputs can easily withstand a
common mode voltage above the positive supply since the
inputs are the emitters of two matched PNP devices (see
Figure 12). This is vital in a system which must operate in
the conditions present under the hood of an automobile.
The inputs can also survive when taken well below ground.
If a negative voltage is present at the inputs of the compara-
tor, the two emitter-base PNP junctions become reverse bi-
ased and block any current flow in or out of the device. To
disable an unused comparator it is recommended that the
inputs be connected to ground.
8
相關PDF資料 |
PDF描述 |
|---|---|
| LM1946N | LM1946 Over/Under Current Limit Diagnostic Circuit |
| LM194 | LM194/LM394 Supermatch Pair |
| LM1950 | 750 mA High Side Switch |
| LM1950T | 750 mA High Side Switch |
| LM1951 | LM1951 Solid State 1 Amp Switch |
相關代理商/技術參數(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 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| LM1949N/NOPB | 功能描述:開關變換器、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 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
發(fā)布緊急采購，3分鐘左右您將得到回復。