Datasheet L4620 Datasheet (SGS Thomson Microelectronics)



DRIVESDIRECTLY300 mAALARMLOAD

.

PROGRAMMABLEINPUTPOLARITYTO

.

ACTIVATETHEOUTPUT STAGE
PROGRAMMABLEDELAYTIME

.

PROGRAMMABLEOUTPUTDUTY CYCLE

.

OUTPUTSHORTCIRCUITPROTECTION

.

OVERVOLTAGEANDTHERMAL

.

PROTECTION

L4620

LIQUIDLEVEL ALARM

Minidip

DESCRIPTION

The L4620is anintegratedcircuit,designedforthe
liquid level control in automotiveapplications. The
liquid level is indicated by an attenuationbetween
transmittedand receivedsignalacrossa sensortip
in thelquid. If the attenuationexceedesan internal
threshold- sensortipoutsidetheliquidorliquidtem­peraturehigherthana determinedvalue- asquare­wave alarm output indicates an unsufficient liquid
condition.Iftheliquidlevelisrestoredbeforetheend
of a delaytime the alarmis notactivated.

Throughtwopinsitis possibletoprogram:thedelay

BLOCK DIAGRAM

ORDERING NUMBER : L4620

time to activate thealarm, the duty cycleof the
output squarewave,the polarity ofthe input thre­sholdof thesensorfor alarmactivation.

TheabovefeaturesmaketheL4620particularlyver­satilefor many applicationsand givethe possibility
tousevarioussensor types.

Internal circuits prevent spurious indications from
the liquid sensor and a latch keeps the alarmacti­vateduntilthesupplyvoltageisswitchedoff.Thede­viceincludesthermalshutdownprotections.

December 1999

1/9

L4620

ABSOLUTE MAXIMUM RATINGS

Symbol Parameter Value Unit

I

V

I

out

P

T

j,Tstg

PI N CONNE CTION (top view)

Supply Current (VS>VZ) 200 mA

S

Sensor Input Voltage (V2High) 7 V

3

Output Current 500 mA
Power Dissipation at T

tot

amb

=70°C

0.8 W

Junction and Storage Temperature Range – 55 to 150

°C

THERMAL DATA

Symbol Parameter Value Unit

Thermal Resistance Junction-ambient Max 100 °

2/9

R

th j-amb

C/W

PIN FUNCTION (BlockDiagram)

L4620

N

°

1 Oscillator A capacitor C

Name Function

connected to ground and a resistor R

osc

voltage) set the frequency of the internal oscillator. The period is given by: T

+ 5000) C

(R

osc

osc

connected to pin 5 (supply

osc

osc

= 0.693

2 Sensor Output A squarewave is available at this pin to drive the external sensor. The output

frequency is 1/32 of the internal oscillator fosc, i.e. 50Hz using the values of

= 180kΩand C

R

osc

= 4.7nF for the external components.

osc

3 Sensor Input Connection for liquid level sensing. During the zero level of the squarewave signal at

pin 2, the internal sensing circuit is disabled. During the high level of the wave shape
the input is compared with a threshold which depends on the output sensor volta

= 0.4V2(typ). If the input voltage becomes higher than the above V

V

SENSH

value is reduced to V

V

sens

= 0.22V2(typ), providing an hysteresis available with

SENSL

SENSH

, the

both the programmable polarities.
4 GND This pin must be connected to ground.
5 Supply Voltage Supply voltage input. A 4.5V (typical) zener is present at the input. The external

resistor limits the current through the zener for high supply voltages. Moreover when

the voltage at this pin is down 2.5V (typical) the internal reset circuit is activated
6 Alarm Driver

Output

7 Alarm Delay

Select

An internal open collector stage is available at this pin to drive the external alarm

indicator by a rectangular waveshape. The output period depends on the external

component R

osc

and C

. Using the recommended values of block diagram th

osc

This program pin selects the alarm delay to activate the output stage after a low liquid

level indication of the sensor. The delay depends on the internal oscillator frequency.

Refer to application circuit, if this pin is kept low the typical delay is 10.
8 Sensor Polarity

Select Output
Duty-cycle
Select

Through this pin it is possible to program both the sensor polarity with respect to the

internal threshold and the duty-cycle of the output waveform which drives the alarm.

When this pin is kept low the output rectangular wave duty cycle is 1:64

(T = 320ms, t = 5ms in fig. 2) and the output is activated, after the delay time, if the

voltage at pin 3 is higher than V

. When the voltage at this pin is high the output

SENS

duty cycle is 50% (t = 160ms) and the output goes on, after the delay

3/9

L4620

ELECTRICAL CHARACTERISTICS (T

=25°C, unless otherwise specified. Refer to block diagram

amb

for externalcomponent values)

Symbol Parameter Test Conditions Min. Typ. Max. Unit

V

I

f

osc

V

7,V8

I

7,I8

V

I

V

SENSH/V2

V

sens

_____

V

V

clamp3L

V

clamp3H

I

sens

Internal Zener Voltage (pin 5) IS= 24 mA 4 4.5 5 V

Z

Supply Current (pin 5) VS= 3.8 V 6.5 11 mA

S

Oscillator Frequency (pin 1)
Programming Pins Input

Voltage (pin 7, 8)
Programming Pins Input Current

(pin 7, 8)
Sensor Drive Output Voltage, (*) V2= Low,

2

Sensor Driver Output Current – 1 1 mA

2

Sensor Input High Threshold
Voltage Versus V

(pin 3)

2

Sensor Input Low Threshold
Voltage Versus V

2

(pin 3)

2

Sensor Input Clamping Voltage
(pin 3)

= 180 kΩ,C

R

osc

osc

= 4.7 nF
Low State 0.3 V
High state 2 V
V7=V8=0V –1
V

7=V8=VZ

=1mA

I

2

= High,

V

2

=1mA

I

2

V

= High

2

V

pin 3<VSENSL

V

= High

2

V

pin 3>VSENSH

– 100µA<I

= Low

V

2

sens

< 100µA

V2= High

= – 100 µA

I

3

I

= + 100µA

3

Sensor Input Bias Current (pin3)V

= High 1.2

sens

1.45 1.6 1.75 kHz

V

–1 VZ–0.4 V

Z

0.33 0.4 0.47

0.15 0.22 0.29

– 0.1 0.1 V

– 0.8 – 0.6 – 0.4 V

V

Z

150

0.4 V

VZ+0.8 V

µA
µA

µA

10.24 sec

V

out(sat)

T

Delay Time f

d

Output Stage Saturation

= 1.6 kHz

osc

= Low

V

7

V

= High 20.48 sec

7

I

= 200 mA 1.3 V

out

Voltage (pin 6) (**)

V

out(clamp)

Output Stage Overvoltage

I

=70mA 19 21 23 V

out

Protection (pin 6)

I

LEAK

*) This is a squarewave signal.The frequencyis given by : f = f

**) The output squarewave signal frequency is given by f = fosc.

The duty cycle depends on the state of the pin 8 and can be or 1 : 2 or 1 : 64, i.e. refer to figure 2, T = 320 ms, t = 160 or 5 ms when
the oscillator frequency f

Leak Current (pin 6) P6 = 15V; P7 = P8 = GND 100 µ

= 1.6 KHz.

osc

512

1

32

1

osc

.

A

4/9

CIRCUI T OPERAT ION

L4620

TheL4620liquid levelalarm isdesignedto operate
witha varietyof sensortypeswhichchangeimped­ancedependingon whetherthesensoris aboveor
belowthelevelofaliquid.Iftheimpedancevariation
of ther liquid itselfis sensed,a very simple sensor
(two electrodes) can be used. The output stage
drivesdirectlythealarmindicatorwitha 300mArec­tangularwavesignal,thedutycycleofwhichispro­grammable.

SENSORINTERFACE.
Asshownintheapplicationcircuit,thesensoriscon-

nectedso thatit variesthe attenuationofa square­wavesignalbetweenpin 2and pin3 whereitsposi­tivehalfcycleiscomparedwiththereferencethresh­old(withhysteresis).

Thisfrequency,generatedinternallyby a 50%duty
cycle oscillator, is 50Hz in the typical application
(R

osc

= 180KΩ C

=4.7nF).

osc

Thethresholdofthesensorinputis afunctionofthe
outputvoltageatpin2.Thehysteresisisprovidedby
a Schmitttriggercomparator.As shownin figure1,
this gives hysteresis with either threshold polarity
selected.

TheACdrivingof thelevel sensorallowsthe useof
a capacitive filter (C

A,CB,CC

in block diagram)
which acts as a bandpass filter at the frequency
used.TheresistorR

intheapplicationcircuitbiases

C

the sensorinputstage. In this waytheinterference
problemstypicalof automotiveapplicationsare re­ducedconsiderably.If,however,itis not necessary
to decoupleand filter the sensor a simple resistive
networkmaybe used,eliminatingthecapacitors.

SPURIOUSINDICATION PROTECTION.
Topreventspuriousalarmsignalswhentheliquidis

agitatedor in the presence of interference,the de­viceincludestwo protectionmechanism:

Firstly,thesensorinterfacewhichsamplestheposi­tivehalfcycleofthesensorsignalactivatesitsoutput
onlyiftherearefourconsecutivealarmconditionin­dications.Secondly,the alarm outputstage is only
activated after an externally programmable delay.
During this delay if the alarm conditionceases the
alarmoutputwill not be activated.

Usingthe values C

= 4.7nF and R

osc

= 180KΩ,

osc

whichgive a typicaloscillatorfrequencyof1.6KHz,
delaysofabout10s (programmingpin7 low)or20s.

INTERNALMEMORY.
Whenthealarm outputhasbeenactivatedaninter-

nal latch holds it in the active state until the power
supply is removed. This feature ensures that the
alarmwillnotbeinterruptedifthesensorconnection
breaks.

OUTPUTSTAGE.
Throughpin8 itispossibleto programthedutycycle

of the alarmsignal waveform(see figure2). When
pin8ishightheoutputsignalhasa dutycycleof50%
; ifpin 8 is low thedutycycle is 1 : 64.The periodof
theoutputsignalisalways320msusingthecompo­nentvaluesindicatedin block diagram.

Theoutputstagecandeliverupto300mAandispro­tectedinternallyagainstovervoltages(bya zener).

A thermalshutdowncircuit providesadditionalpro­tection.

5/9

L4620

SENSOR INPUT WAVEFORM
Figure1a : Pin8 Low; Alarmwith InputVoltage> Threshold.

Figure1b : Pin8 High; AlarmwithInput Voltage< Threshold.

6/9

L4620

Figure2a : OutputAlarm Waveformwith Pin8 High:t = T.

1
2

1

Figure2b : OutputAlarmWaveformwithPin 8 Low: t = T.

64

7/9

L4620

DIM.

MIN. TYP. MAX. MIN. TYP. MAX.

A 3.32 0.131

a1 0.51 0.020

B 1.15 1.65 0.045 0.065
b 0.356 0.55 0.014 0.022

b1 0.204 0.304 0.008 0.012

D 10.92 0.430

E 7.95 9.75 0.313 0.384

e 2.54 0.100
e3 7.62 0.300
e4 7.62 0.300

F 6.6 0.260

I 5.08 0.200
L 3.18 3.81 0.125 0.150
Z 1.52 0.060

mm inch

OUTLINE AND

MECHANICAL DATA

Minidip

8/9

L4620

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the conse­quences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No
license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this
publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMi­croelectronics products are not authorized for use as critical components in life support devices or systems without express written
approval of STMicroelectronics.

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 1999 STMicroelectronics – Printed in Italy – All Rights Reserved

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