PIN FUNCTION (Block Diagram)

N

°

Name

Function

1

Oscillator

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

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

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

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

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

L4620

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