L3845

TRUNK INTERFACE

ON CHIP POLARITY GUARD

MEETS DC LINE CHARACTERISTICS OF

EITHER CCITT AND EIA RS 464 SPECS

PULSE FUNCTION

HIGH AC IMPEDANCE

OFF HOOK-STATUS DETECTION OUTPUT

LOW EXTERNAL COMPONENT COUNT

DESCRIPTION

The circuit provides DC loop termination for ana-

log trunk lines.

The V-I characteristics is equivalent to a fixed

voltage drop (zener like 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 exhibit a very high imped-

ance to all AC signal above a minimum frequency

that is determined by the capacitor itself and by a

20 K nominal resistor integrated on the chip.

The Off-Hook status is detected all the time a

typic of 8 mA is flowing into the circuit. In this con-

dition a constant current generator is activated to

supply an external device (typically an optocou-

pler) without affecting the AC characteristic of the

circuit.

When Pulse Dialing is required the PULSE input

(pin 3) connected to V- causes the device to re-

duce the fixed DC voltage drop and to exhibit a

pure resistive impedance equal to the external re-

sistor.

This is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without notice.

June 1996

POLARITY

GUARD

DC LINE

TERMINATION

OF HOOK

DETECTION

CIRCUIT

1

7

8

3

4

IN1

IN2

562

ACT

DCT

V-

R2

R3

R1

S1

C1

S2

V+

PULSE

HD0

D96TL263

BLOCK DIAGRAM

Minidip

SO8

ORDERING NUMBERS:

L3845B

L3845D

1/7