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PDF L4620 Data sheet ( Hoja de datos )
| Número de pieza | L4620 | |
| Descripción | LIQUID LEVEL ALARM | |
| Fabricantes | STMicroelectronics | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de L4620 (archivo pdf) en la parte inferior de esta página. Total 9 Páginas | ||
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® L4620
. DRIVES DIRECTLY 300 mA ALARM LOAD
. PROGRAMMABLE INPUT POLARITY TO
ACTIVATE THE OUTPUT STAGE
. PROGRAMMABLE DELAY TIME
. PROGRAMMABLE OUTPUT DUTY CYCLE
. OUTPUT SHORT CIRCUIT PROTECTION
. OVERVOLTAGE AND THERMAL
PROTECTION
DESCRIPTION
The L4620 is an integrated circuit, designed for the
liquid level control in automotive applications. The
liquid level is indicated by an attenuation between
transmitted and received signal across a sensor tip
in the lquid. If the attenuation exceedes an internal
threshold- sensortip outsidethe liquid or liquid tem-
peraturehigher than a determinedvalue - a square-
wave alarm output indicates an unsufficient liquid
condition.If the liquid levelis restoredbeforethe end
of a delay time the alarm is not activated.
Throughtwo pins it is possible to program : the delay
BLOCK DIAGRAM
LIQUID LEVEL ALARM
Minidip
ORDERING NUMBER : L4620
time to activate the alarm, the duty cycle of the
output squarewave,the polarity of the input thre-
shold of the sensor for alarm activation.
Theabovefeaturesmake theL4620particularlyver-
satile for many applications and give the possibility
to use various sensor types.
Internal circuits prevent spurious indications from
the liquid sensor and a latch keeps the alarm acti-
vateduntilthe supply voltageis switchedoff.The de-
vice includes thermal shutdown protections.
December 1999
1/9
1 page  
CIRCUIT OPERATION
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 impedancevariation
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 300mArec-
tangularwave signal, the duty cycle of which is pro-
grammable.
SENSOR INTERFACE.
As shownin the applicationcircuit, the sensoris con-
nected so that it varies the attenuation of a square-
wave signal between pin 2 and pin 3 where its posi-
tive halfcycle is comparedwiththe referencethresh-
old (with hysteresis).
This frequency, generated internally by a 50% duty
cycle oscillator, is 50Hz in the typical application
(Rosc = 180KΩ Cosc = 4.7nF).
The threshold of the sensor inputis a function of the
outputvoltageat pin 2. The hysteresisis providedby
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.Theresistor RC in theapplicationcircuit 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.
L4620
SPURIOUS INDICATION PROTECTION.
To preventspurious 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 halfcycleof the sensorsignalactivatesits output
only if there are four consecutive alarm conditionin-
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 = 180KΩ,
which give a typical oscillator frequency of 1.6KHz,
delaysof about10 s (programmingpin 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.
Throughpin 8 it is possibleto programthe duty cycle
of the alarm signal waveform (see figure 2). When
pin 8is high the outputsignalhasa dutycycle of50%
; 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 outputstagecandeliver upto 300mAand ispro-
tected internally against overvoltages (by a zener).
A thermal shutdown circuit provides additional pro-
tection.
5/9
5 Page | ||
| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet L4620.PDF ] | |
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