The L3845 is used for MODEM and PABX Line
Interface applications. The circuit provides DC
loop termination for analog trunk lines. The V/I
characteristic is equivalent to a fixed voltage drop
(zener characteristic) in series with an external resistance
that determines the slope of the DC
characteristic. An external low voltage electrolytic
capacitor causes the circuit to exibit high impedance
to all AC signal in the voice band frequency
range (>20 Kohm). The OFF-HOOK status is detected
when the Line Current is higher than 8
mA. In this condition a constant current generator
is activated to supply an external device (typically
an optocoupler) without affecting the DC/AC characteristics
of the circuit. An additional function is
provided in order to reduce the DC fixed voltage
drop and the AC impedance (PULSE MODE) This
function can be used to respect some European
Countries specifications during Pulse Dialling Operation.