Product Summary

The L3845B1 is a trunk interface. The L3845B1 provides DC loop termination for analog 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 L3845B1 to exhibit a very high impedance 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 condition a constant current generator is activated to supply an external device(typically an optocoupler) without affecting the AC characteristic of the circuit. When Pulse Dialing is required the PULSE input (pin 3) connected to V- causes the L3845B1 to reduce the fixed DC voltage drop and to exhibit a pure resistive impedance equal to the external resistor.

Parametrics

L3845B1 absolute maximum ratings: (1)VL Max Line Voltage (pulse duration 10 ms max): 20 V; (2)IL Max Line Current: 150 mA; (3)Ptot Total Power Dissipation at Tamb = 70 ℃: 800 mW; (4)Top Operating Temperature: - 40 to + 70 ℃; (5)Tsrg, Tj Storage and Junction Temperature: - 55 to + 150 ℃.

Features

L3845B1 features: (1)on chip polarityguard; (2)meets dc line characteristics of; (3)either ccitt and eia rs 464 specs; (4)pulse function; (5)high ac impedance; (6)off hook-status detection output; (7)low external component count.

Diagrams

L3845B1 block diagram

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