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 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 circuit to exhibit a very high impedance to all AC signal above a minimum frequency that is determined by the capacitor itself and 20 K nominal resistor integrated on the chip. The Off-Hook status is detected all the time a typic mA is flowing into the circuit. In this condition a constant current generator is activated to BLOCK DIAGRAM

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 device to reduce the fixed DC voltage drop and to exhibit a pure resistive impedance equal to the external resistor.

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

Symbol VL IL Ptot Top Tsrg, Tj Parameter Max Line Voltage (pulse duration 10 ms max) Max Line Current Total Power Dissipation at Tamb 70 �C Operating Temperature Storage and Junction Temperature Value + 150 Unit mW �C

SUBS = the pin is electrically and thermally in good contact with the chip sustrate. Connect to PCB copper tracks, for heat dissipation the tracks shall preferably be electrically connected to pin 20 (internally bonded to the chip substrate) or left floating. A higher track density and/or area assures a Rth j-amb towards the lower limit.

Symbol VL Parameter Line Voltage (normal mode) Test Condition PULSE = Open 100 mA PULSE mA 6.5 Min. Typ. Max. Unit mA

ON/OFF-Hook Line Current Detection Threshold OFF/ON-Hook Line Current Detection Threshold OFF-Hook Output Drive Current at Pin HDO Pulse Input Low Voltage Pull-up Input Current at Pin PULSE (pulse mode) Imput Current at Pin Pulse (normal mode) 100 mA Pulse 20 mA

Symbol ZL Parameter AC Line Impedance Test Condition S1 = Open, S2 = Open S1 = Open, S2 = Open = 1KHz VAC-L S1 = Closed; S2 = Open VAC-L S1 = Open; S2 = Closed VAC-L 2 2(*) Min. Typ. 20 Max. Unit K

APPLICATION INFORMATION With the use of this circuit it is possible to terminate an analog trunk so that all the DC current component is flowing in the TRUNK TERMINATION CIRCUIT while the AC component is decoupled with a low voltage capacitor and can be used with a small and low cost audio coupler transformer to provide the AC balancing termination and two to four wire conversion. Therefore it is usefull both for MODEM and PABX systems.

Figure 1 gives the typical application circuit it is worth to note that the TRUNK TERMINATION CIRCUIT, together with the LS5018 transient suppressor provides a compact and low cost module fully protected against lightning or overvoltages frequently present on telephone lines. The PULSE input when connected to V- allows the device to reduce the Line Voltage and to show a resistive impedance equal R1 to the line. When PULSE input is left open, this function is disable.