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L4620
LIQUID LEVEL ALARM
.DRI .PROGRAMMABLEI .PROGRAMMABLEDELAYTI .PROGRAMMABLEOUTPUTDUTYCYCLE .OUTPUTSHORTCI .OVERVOLTAGEANDTHERMAL
VES DIRECTLY 300 mA ALARM LOAD NPUT POLARITY TO ACTIVATE THE OUTPUT STAGE ME RCUIT PROTECTION 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 attenuationexceedes an internal threshold - sensor tip outside the liquid or liquid temperature higher than a determined value - a squarewave alarm output indicates an unsufficient liquid condition.If the liquid level is restored beforethe end of a delay time the alarm is not activated. Through two pins it ispossible to program : the delay BLOCK DIAGRAM
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. The above featuresmake the L4620particularly versatile 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 activated untilthe supplyvoltage is switched off. The device includes thermal shutdown protections.
November 1990
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L4620
ABSOLUTE MAXIMUM RATINGS
Symbol IS V3 Iout Ptot Tj, Tstg Supply Current (V S > VZ) Sensor Input Voltage (V2 High) Output Current Power Dissipation at Tamb = 70C Junction and Storage Temperature Range Parameter Value 200 7 500 0.8 - 55 to 150 Unit mA V mA W C
PIN CONNECTION (top view)
THERMAL DATA
Symbol Rth j-amb Parameter Thermal Resistance Junction-ambient Max Value 100 Unit C/W
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L4620
PIN FUNCTION (Block Diagram)
N 1 Name Oscillator Function A capacitor Cosc connected to ground and a resistor R osc connected to pin 5 (supply voltage) set the frequency of the internal oscillator. The period is given by: Tosc = 0.693 (R osc + 5000) Cosc 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 = 180k and C osc = 4.7nF for the external components. 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. This pin must be connected to ground. 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 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 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. 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
2
Sensor Output
3
Sensor Input
4 5
GND Supply Voltage
6
Alarm Driver Output Alarm Delay Select Sensor Polarity Select Output Duty-cycle Select
7
8
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L4620
ELECTRICAL CHARACTERISTICS (Tamb = 25 C, unless otherwise specified. Refer to block diagram for external component values)
Symbol VZ IS fosc V7, V8 I7, I8 V2 Parameter Internal Zener Voltage (pin 5) Supply Current (pin 5) Oscillator Frequency (pin 1) Programming Pins Input Voltage (pin 7, 8) Test Conditions IS = 24 mA VS = 3.8 V Rosc = 180 k, C osc = 4.7 nF Low State High state 2 -1 150 0.4 VZ-1 -1 V2 = High Vpin 3 < VSENSL V2 = High Vpin 3 > VSENSH - 100 A < Isens < 100 A V2 = Low V2 = High I3 = - 100 A I3 = + 100 A Isens Td Sensor Input Bias Current (pin 3) Delay Time Vsens = High fosc = 1.6 kHz V7 = Low V7 = High Vout(sat) Vout (clamp) Output Stage Saturation Voltage (pin 6) (**) Output Stage Overvoltage Protection (pin 6) Iout = 200 mA Iout = 70 mA 19 21 10.24 20.48 1.3 23 0.33 0.15 0.4 0.22 VZ-0.4 1 0.47 0.29 1.45 Min. 4 Typ. 4.5 6.5 1.6 Max. 5 11 1.75 0.3 Unit V mA kHz V V A A V V mA
Programming Pins Input Current V7 = V8 = 0 V (pin 7, 8) V7 = V8 = VZ Sensor Drive Output Voltage, (*) V2 = Low, I2 = 1 mA V2 = High, I2 = 1 mA
I2 VSENSH/V2 Vsens _____ V2 Vclamp3L Vclamp3H
Sensor Driver Output Current Sensor Input High Threshold Voltage Versus V2 (pin 3) Sensor Input Low Threshold Voltage Versus V2 (pin 3) Sensor Input Clamping Voltage (pin 3)
- 0.1 - 0.8 VZ - 0.6
0.1 - 0.4 VZ +0.8 1.2
V V V A sec sec V V
*) This is a squarewave signal. The frequency is given by : f = 1 **) The output squarewave signal frequency is given by f =
1 32
fosc.
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.
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L4620
CIRCUIT OPERATION The L4620 liquid level alarm is designed to operate with a variety of sensor types which change impedance dependingon whether the sensor is aboveor below the level of a liquid. If the impedance variation of ther liquid itself is sensed, a very simple sensor (two electrodes) can be used. The output stage drives directly the alarm indicatorwith a 300mArectangular wave signal, the duty cycle of which is programmable. SENSOR INTERFACE. As shown in the applicationcircuit, the sensor is connected so that it varies the attenuation of a squarewave signal between pin 2 and pin 3 where its positive half cycle is compared with the referencethreshold (with hysteresis). This frequency, generated internally by a 50% duty cycle oscillator, is 50Hz in the typical application (Rosc = 180K Cosc = 4.7nF). The threshold of the sensor input is a functionof the output voltage at pin 2. The hysteresis is provided by 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.The resistor RC in the application circuit 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 prevent spurious 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 half cycle ofthe sensor signal activatesits output only if there are four consecutive alarm condition indications. 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 = 180K, which give a typical oscillator frequency of 1.6KHz, delays of about 10 s (programming pin 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 interruptedif the sensor connection breaks. OUTPUT STAGE. Throughpin 8 it is possible to program the duty cycle of the alarm signal waveform (see figure 2). When pin 8 is highthe output signal hasa dutycycle of 50% ; 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 output stage can deliver up to 300mA and is protected internally against overvoltages (by a zener). A thermal shutdown circuit provides additional protection.
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L4620
SENSOR INPUT WAVEFORM Figure 1a : Pin 8 Low ; Alarm with Input Voltage > Threshold.
Figure 1b : Pin 8 High ; Alarm with Input Voltage < Threshold.
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L4620
1
Figure 2a : Output Alarm Waveform with Pin 8 High : t =
2
T.
Figure 2b : Output Alarm Waveform with Pin 8 Low : t =
1 64
T.
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L4620
MINIDIP MECHANICAL DATA
mm DIM. A a1 B b b1 D E e e3 e4 F I L Z 3.18 7.95 2.54 7.62 7.62 6.6 5.08 3.81 1.52 0.125 0.51 1.15 0.356 0.204 1.65 0.55 0.304 10.92 9.75 0.313 0.100 0.300 0.300 0.260 0.200 0.150 0.060 MIN. TYP. 3.32 0.020 0.045 0.014 0.008 0.065 0.022 0.012 0.430 0.384 MAX. MIN. inch TYP. 0.131 MAX.
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Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics 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 SGS-THOMSON Microelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of SGS-THOMSON Microelectronics. (c) 1995 SGS-THOMSON Microelectronics - All Rights Reserved SGS-THOMSON Microelectronics GROUP OF COMPANIES Australia - Brazil - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco - The Netherlands - Singapore Spain - Sweden - Switzerland - Taiwan - Thaliand - United Kingdom - U.S.A.
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