APPLICATION CIRCUIT DIAGRAM

Figure 1 : Typical application diagram for the L9704 circuit. The current flowing in the arrow direction is as-

the corresponding pins.

FUNCTIONAL DESCRIPTION

The L9704 circuit monitors the status of the contacts

connectedto battery and through the series external

contacts equivalent circuit is supposed to be as

shown in fig. 2.

The L9704 circuit compares the input current with

the current through the internal reference resistor.

The device is designed to work with an externalinput

Ω. With thisinputresistor

the contact current, when the contact is closed and

the device activated (EN = LOW) is

1K

Ω

(1)

tion voltage of 2V) was considered so that the lowest

The function of the circuit can be demonstrated with

the transfer characteristics, showing the output

contact :

(2)

and for the open contact :

(3)

The output goes HIGH when the input resistance in-

creases above 6.5k

Ω (typicalvalue) and goesLOW,

when the input resistance decreases below 4.8K

Ω

Ω for

Ω for HIGH implies that a contact

Ω will

be recognized as OFF = HIGH. These limits are

valid within the supply voltage range 5V

the

battery

voltage

potential

difference

of

battery protection diode D1 voltage from 0.5V to 1V.

L9704

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