FUNCTIONAL DESCRIPTION

The L9703 circuit monitors the status of the contacts

connected to ground and through this series exter-

contacts equivalent circuit is supposed to be as

shown in fig. 2.

The L9703 circuit compares the input current with

the current through the internal reference resistor.

The device is designed to work with an external input

Ω. With this inputresistor

the contact current, when the contact is closed and

the device activated (EN = LOW) is

1k

Ω

(1)

saturation voltage of 2V was considered so that the

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 above5.3k

Ω (typicalvalue) and goes LOW,

when the input resistance decreases below 4k

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 6V

≤ VS ≤ 16V

and

the

ground

potential

difference

of

∆VGND = 0,1V.

The internal clamping diodes at the contact moni-

toring inputs, together with the external contacts se-

transientsat the contactconnection.The contactse-

sient.

The dynamic behaviour of the circuit is defined by

fined only by the internal circuitry. In both cases, an

external output capacitance less than 50pF is as-

sumed, the internal output capacitances of the

three-state buffers are less than 5pF.

Figure 2 : The Contact Sense Input Connection with the Contact Equivalent Circuit.

L9703

5/9