MSAN-156 Datasheet | Mitel Networks

Application Note Implementation Details for the MH88617 SLIC AN5028 ISSUE 2 September 1998 Contents 1. Overview 2. Loop Current 2.1 Programming 2.2 Power Down 2.3 Overcurrent Fault Protection 3. Ringing 3.1 Supply voltages 3.2 Square wave ringing 4. Gain, Input and Balance Impedances 4.1 Programming 4.2 VX and VR signals 5. Metering Injection 6. Relay Drive 7. Protection 8. Power supply considerations 1.0 Overview The MH88617 is a highly featured Subscriber Line Interface Circuit (SLIC). It provides a total analogue transmission and signalling link between a switching system and a subscriber loop. Typical applications include PABX and Key Telephone Systems, Analog Terminal Adaptors, Pair Gain, Fibre in the Loop and Wireless Local Loop systems. This Application Note is intended to assist the user in implementing the MH88617 as an analogue line interface ponent in a munications system and should be read in conjunction with the data sheet for the MH88617. 2.0 Loop Current The MH88617 employs a plex feedback network to provide a constant current feed to the line. The loop current can be programmed, via the ’LCA’ pin, between 14m A and 55m A. 2.1 Programming The MH88617 is designed to provide 24m A of constant loop current by simply leaving the LCA pin open circuit. The loop current can be programmed above 24m A by connecting a resistor between LCA and VCC. Similarly, to program the loop current below 24m A a resistor needs to be connected between LCA and GND. Internally, the MH88617 LCA pin can be depicted as shown in Figure 1. MH88617 Application Note Loop current m A R (Kohm) 4.0 12.0 261.6 40.1 20.7 13.5 15 20 25 13k RLCA RTOTAL 30 35 40 Table 1 - Value of RLCA for Given Loop Current It should be noted that if the loop current reaches 100m A, the device will shut down, due to its internal protection circuit. Also, if the loop current falls below 12m A, SHK will cease to function. If the loop length is too long, the...