L4620 LIQUID LEVEL ALARM .. .. .. 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 temperaturehigher than a determinedvalue - a squarewave 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 Minidip ORDERING NUMBER : L4620 time to activate the alarm, the duty cycle of the output squarewave,the polarity of the input threshold of the sensor for alarm activation. Theabovefeaturesmake theL4620particularlyversatile 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 activateduntilthe supply voltageis switchedoff.The device includes thermal shutdown protections. BLOCK DIAGRAM December 1999 1/9 L4620 ABSOLUTE MAXIMUM RATINGS Symbol Parameter IS Supply Current (VS > VZ) V3 Sensor Input Voltage (V2 High) Iout Ptot Tj, Tstg Value Unit 200 mA 7 V Output Current 500 mA Power Dissipation at Tamb = 70°C 0.8 W – 55 to 150 °C Junction and Storage Temperature Range PIN CONNECTION (top view) THERMAL DATA Symbol Rth j-amb 2/9 Parameter Thermal Resistance Junction-ambient Max Value Unit 100 °C/W L4620 PIN FUNCTION (Block Diagram) Name N° 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 Rosc = 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 Output 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 Rosc and Cosc. Using the recommended values of block diagram th 7 Alarm Delay Select 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 VSENS. When the voltage at this pin is high the output duty cycle is 50% (t = 160ms) and the output goes on, after the delay 3/9 L4620 ELECTRICAL CHARACTERISTICS (Tamb = 25 °C, unless otherwise specified. Refer to block diagram for external component values) Symbol Parameter Test Conditions VZ Internal Zener Voltage (pin 5) IS = 24 mA IS Supply Current (pin 5) VS = 3.8 V fosc V7 , V 8 I7, I8 V2 Oscillator Frequency (pin 1) Rosc = 180 kΩ, Cosc = 4.7 nF Programming Pins Input Voltage (pin 7, 8) Low State High state Programming Pins Input Current V7 = V8 = 0 V (pin 7, 8) V7 = V8 = VZ Min. Typ. Max. Unit 4 4.5 5 V 1.45 6.5 11 mA 1.6 1.75 kHz 0.3 V 2 V –1 µA Sensor Drive Output Voltage, (*) V2 = Low, I2 = 1 mA V2 = High, I2 = 1 mA VZ–1 µA 0.4 V VZ–0.4 V 1 mA I2 Sensor Driver Output Current VSENSH/V2 Sensor Input High Threshold Voltage Versus V2 (pin 3) V2 = High Vpin 3 < VSENSL 0.33 0.4 0.47 V sens _____ V2 Sensor Input Low Threshold Voltage Versus V2 (pin 3) V2 = High Vpin 3 > VSENSH 0.15 0.22 0.29 Sensor Input Clamping Voltage (pin 3) – 100 µA < Isens < 100 µA V2 = Low – 0.1 V2 = High I3 = – 100 µA – 0.8 I3 = + 100 µA VZ Vclamp3L Vclamp3H Isens Td Vout(sat) Vout(clamp) ILEAK –1 150 – 0.6 Sensor Input Bias Current (pin 3) Vsens = High Delay Time fosc = 1.6 kHz V7 = Low 10.24 V7 = High 20.48 Output Stage Saturation Voltage (pin 6) (**) Iout = 200 mA Output Stage Overvoltage Protection (pin 6) Iout = 70 mA Leak Current (pin 6) P6 = 15V; P7 = P8 = GND *) This is a squarewave signal. The frequency is given by : f = 1 19 21 0.1 V – 0.4 V VZ +0.8 V 1.2 µA sec sec 1.3 V 23 V 100 µA fosc. 32 1 **) 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. 4/9 L4620 CIRCUIT OPERATION The L4620 liquid level alarm is designed to operate with a variety of sensor types which change impedance 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 300mArectangularwave signal, the duty cycle of which is programmable. SENSOR INTERFACE. As shownin the applicationcircuit, the sensoris connected so that it varies the attenuation of a squarewave signal between pin 2 and pin 3 where its positive halfcycle is comparedwiththe referencethreshold (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 reduced 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 preventspurious alarm signals when the liquid is agitated or in the presence of interference, the device includes two protection mechanism : Firstly, the sensor interface which samples the positive halfcycleof the sensorsignalactivatesits output only if there are four consecutive alarm conditionindications. 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 internal 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 component values indicated in block diagram. The outputstagecandeliver upto 300mAand isprotected internally against overvoltages (by a zener). A thermal shutdown circuit provides additional protection. 5/9 L4620 SENSOR INPUT WAVEFORM Figure 1a : Pin 8 Low ; Alarm with Input Voltage > Threshold. Figure 1b : Pin 8 High ; Alarm with Input Voltage < Threshold. 6/9 L4620 1 Figure 2a : OutputAlarm Waveform with Pin 8 High : t = Figure 2b : OutputAlarm Waveform with Pin 8 Low : t = 2 1 64 T. T. 7/9 L4620 mm DIM. MIN. A TYP. MAX. MIN. 3.32 TYP. MAX. 0.51 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 E 0.020 10.92 7.95 9.75 0.430 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 Z 3.18 OUTLINE AND MECHANICAL DATA 0.131 a1 D 8/9 inch 3.81 1.52 0.125 0.150 0.060 Minidip 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. The ST logo is a registered trademark of STMicroelectronics 1999 STMicroelectronics – Printed in Italy – All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - China - Finland - France - Germany - Hong Kong - India - Italy - Japan - Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdom - U.S.A. http://www.st.com 9/9