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參數資料
| 型號： | L4620 |
| 廠商： | STMICROELECTRONICS |
| 元件分類： | 消費家電 |
| 英文描述： | SPECIALTY CONSUMER CIRCUIT, PDIP8 |
| 封裝： | MINI, DIP-8 |
| 文件頁數： | 5/9頁 |
| 文件大小： | 185K |
| 代理商： | L4620 |
The L4620 liquid level alarm is designed to operate
with a variety of sensor types which change imped-
ance depending on whether the sensor is above or
below the level of a liquid. If the impedance variation
of ther liquid itself is sensed, a very simple sensor
(two electrodes) can be used. The output stage
drives directly the alarm indicator with a 300mA rec-
tangular wave signal, the duty cycle of which is pro-
grammable.
SENSOR INTERFACE.
As shown in the application circuit, the sensor is con-
nected so that it varies the attenuation of a square-
wave signal between pin 2 and pin 3 where its posi-
tive half cycle is compared with the reference thresh-
old (with hysteresis).
This frequency, generated internally by a 50% duty
cycle oscillator, is 50Hz in the typical application
(Rosc = 180K
Cosc = 4.7nF).
The threshold of the sensor input is a function of the
output voltage at pin 2. The hysteresis is provided by
a Schmitt trigger comparator. As shown in figure 1,
this gives hysteresis with either threshold polarity
selected.
The AC driving of the level sensor allows the use of
a capacitive filter (CA, CB, CC in block diagram)
which acts as a bandpass filter at the frequency
used. The resistor RC in the application circuit biases
the sensor input stage. In this way the interference
problems typical of automotive applications are re-
duced considerably. If, however, it is not necessary
to decouple and filter the sensor a simple resistive
network may be used, eliminating the capacitors.
SPURIOUS INDICATION PROTECTION.
To prevent spurious alarm signals when the liquid is
agitated or in the presence of interference, the de-
vice includes two protection mechanism :
Firstly, the sensor interface which samples the posi-
tive half cycle of the sensor signal activates its output
only if there are four consecutive alarm condition in-
dications. Secondly, the alarm output stage is only
activated after an externally programmable delay.
During this delay if the alarm condition ceases the
alarm output will not be activated.
Using the values Cosc = 4.7nF and Rosc = 180K
,
which give a typical oscillator frequency of 1.6KHz,
delays of about 10 s (programming pin 7 low) or 20s.
INTERNAL MEMORY.
When the alarm output has been activated an inter-
nal latch holds it in the active state until the power
supply is removed. This feature ensures that the
alarm will not be interrupted if the sensor connection
breaks.
OUTPUT STAGE.
Through pin 8 it is possible to program the duty cycle
of the alarm signal waveform (see figure 2). When
pin 8 is high the output signal has a duty cycle of 50%
; if pin 8 is low the duty cycle is 1 : 64. The period of
the output signal is always 320ms using the compo-
nent values indicated in block diagram.
The output stage can deliver up to 300mA and is pro-
tected internally against overvoltages (by a zener).
A thermal shutdown circuit provides additional pro-
tection.
CIRCUIT OPERATION
L4620
5/9
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相關代理商/技術參數 |
參數描述 |
|---|---|
| L465 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:LINEAR INTEGRATED CIRCUITS |
| L-465 | 制造商:RHOMBUS-IND 制造商全稱:Rhombus Industries Inc. 功能描述:TOROID INDUCTOR |
| L465A | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:LINEAR INTEGRATED CIRCUITS |
| L-466 | 制造商:RHOMBUS-IND 制造商全稱:Rhombus Industries Inc. 功能描述:TOROID INDUCTOR |
| L-467 | 制造商:RHOMBUS-IND 制造商全稱:Rhombus Industries Inc. 功能描述:LOW COST POWER INDUCTOR |
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