L4620

L4620 STMICROELECTRONICS | Alldatasheet

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Technical content

.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 .OVERVOLTAGEAND THERMAL PROTECTION

DESCRIPTION

The L4620 is an integratedcircuit, designedfor 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 attenuationexceedesan internal threshold- sensortip outsidethe liquidor liquid tem- peraturehigherthana determinedvalue - a square- wave alarm output indicates an unsufficient liquid condition.Ifthe liquidlevelis restoredbeforetheend of a delay time the alarm is not activated. Throughtwopinsit is possibletoprogram:the delay time to activate the alarm, the duty cycle of the output squarewave,the polarity ofthe input thre- shold of the sensor for alarm activation. TheabovefeaturesmaketheL4620particularlyver- 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- vateduntilthesupplyvoltageis switchedoff.Thede- vice includes thermal shutdown protections. Minidip ORDERING NUMBER : L4620 BLOCK DIAGRAM

Symbol Parameter Value Unit IS Supply Current (VS >V Z) 200 mA V3 Sensor Input Voltage (V2 High) 7 V Iout Output Current 500 mA Ptot Power Dissipation at Tamb =7 0°C 0.8 W Tj,T stg Junction and Storage Temperature Range – 55 to 150 °C PIN CONNECTION (top view) THERMAL DATA Symbol Parameter Value Unit R th j-amb Thermal Resistance Junction-ambient Max 100 °C/W L4620

PIN FUNCTION (Block Diagram) N ° Name Function

1 Oscillator A capacitor C osc connected to ground and a resistor Rosc connected to pin 5 (supply

voltage) set the frequency of the internal oscillator. The period is given by: Tosc = 0.693 (Rosc + 5000) Cosc 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 R osc = 180kΩ and Cosc = 4.7nF for the external components. 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 VSENSH = 0.4V2 (typ). If the input voltage becomes higher than the above VSENSH , the Vsens value is reduced to VSENSL = 0.22V2 (typ), providing an hysteresis available with 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

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 Cosc. Using the recommended values of block diagram th

7 Alarm Delay

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

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 SENS . When the voltage at this pin is high the output duty cycle is 50% (t = 160ms) and the output goes on, after the delay L4620

1*) This is a squarewave signal. The frequency is given by : f = fosc. **) The output squarewave signal frequency is given by f = fosc. 512 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 fosc = 1.6 KHz. ELECTRICAL CHARACTERISTICS (Tamb =2 5°C, unless otherwise specified. Refer to block diagram for external component values) Symbol Parameter Test Conditions Min. Typ. Max. Unit VZ Internal Zener Voltage (pin 5) IS = 24 mA 4 4.5 5 V IS Supply Current (pin 5) V S = 3.8 V 6.5 11 mA fosc Oscillator Frequency (pin 1)R osc = 180 kΩ ,C osc = 4.7 nF 1.45 1.6 1.75 kHz V7,V 8 Programming Pins Input Voltage (pin 7, 8) Low State 0.3 V High state 2 V I7,I8 Programming Pins Input Current (pin 7, 8) V7 =V 8 =0V –1 µA V7 =V 8 =V Z 150 µA V2 Sensor Drive Output Voltage, (*) V2 = Low, I2 =1m A 0.4 V V2 = High, I2 =1m A VZ–1 V Z–0.4 V I2 Sensor Driver Output Current – 1 1 mA VSENSH /V2 Sensor Input High Threshold Voltage Versus V2 (pin 3) V2 = High Vpin 3<V SENSL 0.33 0.4 0.47 V sens Sensor Input Low Threshold Voltage Versus V 2 (pin 3) V2 = High Vpin 3>V SENSH 0.15 0.22 0.29 Vclamp3L Sensor Input Clamping Voltage (pin 3) – 100µA<I sens < 100µA V2 = Low – 0.1 0.1 V Vclamp3H V2 = High I3 = – 100µA I3 = + 100µA VZ VZ +0.8 V Isens Sensor Input Bias Current (pin Vsens = High 1.2 µA Td Delay Time f osc = 1.6 kHz V7 = Low 10.24 sec V7 = High 20.48 sec Vout(sat) Output Stage Saturation Voltage (pin 6) (**) Iout = 200 mA 1.3 V Vout(clamp) Output Stage Overvoltage Protection (pin 6) Iout =7 0m A 1 9 2 1 2 3 V ILEAK Leak Current (pin 6) P6 = 15V; P7 = P8 = GND 100 µA L4620

The L4620 liquid level alarm is designed to operate with a variety of sensor types which change imped- ance dependingon whether the sensor is aboveor below thelevel of a liquid.Ifthe impedancevariation of ther liquid itself is sensed, a very simple sensor (two electrodes) can be used. The output stage drives directly the alarm indicatorwith a 300mArec- tangularwave signal, the duty cycle of which is pro- grammable. SENSOR INTERFACE. As shownin theapplicationcircuit,the sensoris con- nected so that it varies the attenuation of a square- wavesignal between pin 2 and pin 3 whereits posi- tivehalfcycleis comparedwiththereferencethresh- old (with hysteresis). This frequency,generated internally by a 50% duty cycle oscillator, is 50Hz in the typical application osc = 180KΩ Cosc = 4.7nF). The threshold of the sensor inputis a function of the outputvoltageat pin2.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 (C A,C B,C C in block diagram) which acts as a bandpass filter at the frequency used.TheresistorR C intheapplicationcircuitbiases the sensor input stage. In this way the interference problems typical of automotive applications are re- ducedconsiderably. 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 preventspuriousalarm signalswhen the liquid is agitated or in the presence of interference, the de- vice includes two protection mechanism: Firstly,the sensorinterface whichsamples the posi- tivehalfcycleof thesensorsignalactivatesits output only if there are fourconsecutive alarmconditionin- 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 C osc = 4.7nF and Rosc = 180KΩ , which give a typical oscillator frequency of 1.6KHz, delaysofabout10 s (programmingpin 7 low)or 20s. INTERNAL MEMORY. When the alarm outputhas been activatedan inter- nal latch holds it in the active state until the power supply is removed. This feature ensures that the alarmwill not be interruptedifthe sensorconnection breaks. OUTPUT STAGE. Throughpin 8 it is possibleto programthedutycycle of the alarm signal waveform (see figure 2). When pin8is hightheoutputsignalhasa dutycycleof50% ; if pin 8 is low the duty cycle is 1 : 64. The period of the outputsignalis always 320ms using the compo- nent values indicated in block diagram. Theoutputstagecandeliverupto300mAand ispro- tected internally against overvoltages(by a zener). A thermal shutdown circuit provides additional pro- tection. CIRCUIT OPERATION L4620

DIM. mm inch 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 OUTLINE AND MECHANICAL DATA L4620

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