L7583A

Stresses in excess of the absolute maximum ratings can cause permanent damage to the device. These are abso-lute stress ratings only. Functional operation of the device is not implied at these or any other conditions in excess
of those given in the operational sections of the data sheet. Exposure to absolute maximum ratings for extended periods can adversely affect device reliability.

The L7583A/B/C/D Line Card Access Switch is a monolithic solid-state device providing the equivalent switching functionality of three 2 form C switches. The L7583 is designed to provide power ringing access, line test access (test out), and SLIC test access (test in) to tip and ring in central office, digital loop carrier, private branch exchange, digitally added main line, and hybrid fiber coax/fiber-in-the-loop ana-log line card applications. An additional pair of solid-state contacts are also available to provide access for testing of the ringing generator.

The L7583A/B has seven states: the idle talk state (line break switches closed, all other switches open), the power ringing state (ringing access switches closed, all other switches open), loop access state (loop access switches closed, all switches open), SLIC test state (test in switches closed, all other switches open), simultaneous loop and SLIC access state (loop and test in switches closed, all others open), ringing generator test state (ring test switches closed, all others open), and an all OFF state. The seven states in the L7583A/B are also in the L7583C/D, with an additional simultaneous test-out and ring-test state, making the L7583C/D appro-priate for digital loop carrier and other Bellcore TR-57 applications.

The L7583 offers break-before-make or make-before-break switching, with simple logic level input control. Because of the solid-state construction, volt-age transients generated when switching into an inductive ringing lead during ring cadence or ring trip are minimized, possibly eliminating the need for external zero cross switching circuitry. State control is via logic level inputs, so no additional driver cir-cuitry is required.

The line break switch is a linear switch that has exceptionally low ON-resistance and an excellent ON-resistance matching characteristic. The ringing access switch has a breakdown voltage rating >480 V which is sufficiently high, with proper protec-tion, to prevent breakdown in the presence of a tran-sient fault condition (i.e., passing the transient on to the ringing generator).

Incorporated into the L7583Axx and L7583Cxx is a diode bridge/SCR clamping circuit, current-limiting circuitry, and a thermal shutdown mechanism to pro-vide protection to the SLIC device and subsequent circuitry during fault conditions. This is shown in Fig-ure 1 as version A. Positive and negative lightning is
reduced by the current-limiting circuitry and steered to ground via diodes and the integrated SCR. Power cross is also reduced by the current-limiting and ther-mal shutdown circuits.