L3845 Datasheet, PDF (1/7 Pages) STMicroelectronics – TRUNK INTERFACE

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
BLOCK DIAGRAM
Minidip
SO8
ORDERING NUMBERS:
L3845B
L3845D
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.
1
IN1
7
IN2
POLARITY
GUARD
DC LINE
TERMINATION
5
ACT
R2
6
DCT
R3 S2
C1
R1
S1
OF HOOK
DETECTION
CIRCUIT
2
V-
8
V+
3
PULSE
4
HD0
D96TL263
June 1996
1/7
This is advanced information on a new product now in development or undergoing evaluation. Details are subject to change without notice.