L4620 ,LIQUID LEVEL ALARMblock diagramambfor external component values)Symbol Parameter Test Conditions Min. Typ. Max. UnitV ..
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L4620
LIQUID LEVEL ALARM
December 1999
L4620LIQUID LEVEL ALARM DRIVES DIRECTLY 300 mA ALARM LOAD. PROGRAMMABLE INPUTPOLARITYTO
ACTIVATE THE OUTPUT STAGE. PROGRAMMABLE DELAYTIME. PROGRAMMABLE OUTPUT DUTY CYCLE. OUTPUT SHORT CIRCUIT PROTECTION. OVERVOLTAGE AND THERMAL
PROTECTION
DESCRIPTIONThe L4620isan integratedcircuit, designedfor the
liquid level controlin automotive applications. The
liquid levelis indicatedbyan attenuation between
transmitted and received signal acrossa sensortip thelquid.If the attenuationexceedesan internal
threshold- sensortipoutsidetheliquidor liquidtem-
peraturehigherthana determinedvalue- asquare-
wave alarm output indicatesan unsufficient liquid
condition.Ifthe liquid levelisrestoredbeforetheenda delaytime the alarmis not activated.
Throughtwopins itis possibletoprogram: thedelay
timeto activate the alarm, the duty cycleof the
output squarewave,the polarity ofthe input thre-
sholdof the sensorfor alarm activation.
TheabovefeaturesmaketheL4620particularlyver-
satilefor many applicationsand give the possibility use various sensor types.
Internal circuits prevent spurious indications from
the liquid sensor anda latch keeps the alarm acti-
vateduntilthesupplyvoltageisswitchedoff.Thede-
vice includes thermal shutdown protections.
Minidip
ORDERING NUMBER: L4620
BLOCK DIAGRAM1/9
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit Supply Current (VS >VZ) 200 mA Sensor Input Voltage(V2 High) 7 V
Iout Output Current 500 mA
Ptot Power Dissipationat Tamb =70°C 0.8 W
Tj,Tstg Junction and Storage Temperature Range –55to 150 °C
PIN CONNECTION (top view)
THERMAL DATA
Symbol Parameter Value Unit
Rth j-amb Thermal Resistance Junction-ambient Max 100 °C/W
L46202/9
PIN FUNCTION (Block Diagram)
Name Function Oscillator A capacitor Cosc connectedto ground anda resistor Rosc connectedtopin5 (supply
voltage) setthe frequencyof the internal oscillator. The periodis given by: Tosc= 0.693
(Rosc+ 5000) Cosc Sensor Output A squarewaveis availableat thispinto drivethe external sensor. The output
frequencyis 1/32of the internal oscillator fosc, i.e. 50Hz using the valuesof
Rosc= 180kΩ and Cosc= 4.7nFfor the external components. Sensor Input Connectionfor liquid level sensing. During the zero levelof the squarewave signalat
pin2, the internal sensing circuitis disabled. During the high levelof the wave shape
the inputis compared witha threshold which dependson the output sensor volta
VSENSH= 0.4V2 (typ).Ifthe input voltage becomes higher than the above VSENSH, the
Vsens valueis reducedto VSENSL= 0.22V2 (typ), providingan hysteresis available with
both the programmable polarities. GND Thispin mustbe connectedto ground. Supply Voltage Supply voltage input.A 4.5V (typical) zeneris presentat the input. The external
resistor limitsthe current through the zenerfor high supply voltages. Moreover when
the voltageat this pinis down 2.5V (typical)the internal reset circuitis activated Alarm Driver
Output internal open collector stageis availableat this pinto drive the external alarm
indicatorbya rectangular waveshape. The output period dependson the external
component Rosc and Cosc. Using the recommended valuesof block diagramth Alarm Delay
Select
This programpin selects the alarm delayto activate the output stage aftera low liquid
level indicationofthe sensor. The delay dependson the internal oscillator frequency.
Referto application circuit,if thispinis kept low the typical delayis 10. Sensor Polarity
Select Output
Duty-cycle
Select
Through thispinitis possibleto program boththe sensor polarity with respectto the
internal threshold and the duty-cycleof the output waveform which drives the alarm.
When thispinis kept low the output rectangular wave duty cycleis 1:64= 320ms,t= 5msin fig.2) and the outputis activated, afterthe delay time,if the
voltageatpin3is higher than VSENS. When the voltageat this pinis high the output
duty cycleis 50%(t= 160ms) and the output goes on, afterthe delay
L46203/9
*) Thisisa squarewave signal. The frequencyis givenby:f= fosc.**) The output squarewavesignal frequencyis givenbyf= fosc.
The duty cycle dependsonthe stateofthepin8 andcanbeor1:2or1:64,i.e. referto figure2,T= 320ms,t= 160or5ms when
the oscillator frequencyfosc=1.6 KHz.
ELECTRICAL CHARACTERISTICS (Tamb =25 °C, unless otherwise specified. Referto block diagram
for external component values)
Symbol Parameter Test Conditions Min. Typ. Max. Unit Internal Zener Voltage (pin5) IS=24 mA 4 4.5 5 V Supply Current (pin5) VS= 3.8V 6.5 11 mA
fosc Oscillator Frequency (pin1) Rosc= 180 kΩ,Cosc= 4.7nF 1.45 1.6 1.75 kHz
V7,V8 Programming Pins Input
Voltage (pin7,8)
Low State 0.3 V
High state 2 V
I7,I8 Programming Pins Input Current
(pin7,8) =V8 =0V –1 μA =V8 =VZ 150 μA Sensor Drive Output Voltage,(*) V2= Low, =1 mA
0.4 V= High, =1 mA
VZ–1 VZ–0.4 V Sensor Driver Output Current –1 1 mA
VSENSH/V2 Sensor Input High Threshold
Voltage VersusV2 (pin3)= High
Vpin3
0.33 0.4 0.47
Vsens
_____
Sensor Input Low Threshold
Voltage VersusV2 (pin3)= High
Vpin3 >VSENSH
0.15 0.22 0.29
Vclamp3L Sensor Input Clamping Voltage
(pin3) 100 μAVclamp3H V2= High=– 100μA0.8 –0.6 – 0.4 V=+ 100μA VZ VZ +0.8 V
Isens Sensor Input Bias Current (pin
Vsens= High 1.2 μA Delay Time fosc= 1.6 kHz= Low
10.24 sec= High 20.48 sec
Vout(sat) Output Stage Saturation
Voltage (pin6) (**)
Iout= 200 mA 1.3 V
Vout(clamp) Output Stage Overvoltage
Protection (pin6)
Iout =70 mA 19 21 23 V
ILEAK Leak Current (pin6) P6= 15V;P7=P8= GND 100 μA
L4620
4/9
The L4620 liquid level alarmis designedto operate
witha varietyof sensortypeswhich changeimped-
ancedependingon whether the sensoris aboveor
belowthe levelofa liquid.Ifthe impedancevariation ther liquid itselfis sensed,a very simple sensor
(two electrodes) can be used. The output stage
drives directly thealarm indicator witha 300mArec-
tangularwave signal, the dutycycleof whichis pro-
grammable.
SENSOR INTERFACE. shownin theapplicationcircuit,the sensoriscon-
nectedso thatit varies the attenuationofa square-
wave signalbetween pin2 and pin3 whereits posi-
tivehalfcycleiscomparedwiththereferencethresh-
old (withhysteresis).
This frequency,generatedinternallybya 50% duty
cycle oscillator,is 50Hzin the typical application
(Rosc= 180KΩ Cosc= 4.7nF).
The thresholdofthe sensor inputis afunctionof the
outputvoltageatpin2.The hysteresisis providedby Schmitt trigger comparator.As shownin figure1,
this gives hysteresis with either threshold polarity
selected.
The AC drivingof thelevel sensor allows the useof capacitive filter (CA,CB,CCin block diagram)
which acts asa bandpass filterat the frequency
used.TheresistorRC intheapplicationcircuitbiases
the sensor input stage.In this way the interference
problems typicalof automotive applications arere-
ducedconsiderably.If, however,itis not necessary decouple and filter the sensora simple resistive
networkmaybe used,eliminating the capacitors.
SPURIOUS INDICATION PROTECTION. preventspuriousalarm signalswhentheliquidis
agitatedorin the presenceof interference, the de-
vice includestwo protectionmechanism:
Firstly,the sensor interfacewhichsamplesthe posi-
tivehalfcycleof thesensorsignalactivatesitsoutput
onlyif there are four consecutive alarmconditionin-
dications. Secondly, the alarm output stageis only
activated afteran externally programmable delay.
During this delayif the alarm condition ceases the
alarmoutput will notbe activated.
Using the values Cosc= 4.7nF and Rosc= 180KΩ,
which givea typical oscillator frequencyof 1.6KHz,
delaysofabout10s (programmingpin7low)or 20s.
INTERNAL MEMORY.
When the alarm outputhas beenactivatedan inter-
nal latch holdsitin the active state until the power
supplyis removed. This feature ensures that the
alarmwill not beinterruptedifthe sensorconnection
breaks.
OUTPUT STAGE.
Throughpin8 itis possibletoprogramthe dutycycle the alarm signal waveform (see figure2). When
pin8ishightheoutputsignalhasa dutycycleof50% ifpin8is low the duty cycleis1: 64. The periodof
the outputsignalisalways 320msusingthe compo-
nent values indicatedin block diagram.
Theoutputstagecandeliverupto300mAandispro-
tectedinternally against overvoltages(bya zener). thermal shutdowncircuit provides additionalpro-
tection.
CIRCUIT OPERATION
L4620
5/9
SENSOR INPUT WAVEFORM
Figure1a: Pin8 Low; Alarm with Input Voltage> Threshold.
Figure1b: Pin8 High ;Alarm with Input Voltage< Threshold.
L4620
6/9
