Protection solution for line card access switches

31 October 2007 Circuit & System Protection

Solid-state hook switches or LCAS (line card access switches) have been deployed as a space-saving solution in telephone exchanges since the mid 1990s. These devices are a combination of electronic switches replacing traditional electro-mechanical relays. The Bourns TISP4A250H3BJR-S is designed to lower stress to the Le75 series LCASs under AC and lightning impulse conditions and extend the range of TISP4A270H3BJR and TISP4A265H3BJR specifically designed to utilise maximum ringing with other LCAS solutions.

The TISP4A250H3BJR-S has an asymmetrical voltage characteristic with VDRM/V(BO) characteristics of +100 V/+125 V and -200 V/-250 V. This helps to ensure that maximum system voltages may be used while not overstressing the LCAS switches during over-voltage fault conditions on the telephone line. The tight VDRM and V(BO) ratio allows for extended ring voltages to be used while still offering LCAS protection.

The TISP4A250H3BJR-S is manufactured with an ion implant process to provide an accurate voltage protection window in each quadrant. It has also been specifically designed to have an impulse rating of 500 A for a 2/10 μs surge waveshape and 100 A for a 10/1000 μs waveshape.

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