Le75181
PRODUCT DESCRIPTION
Data Sheet
The Le75181 Ringing Access Switch is a monolithic solid-state device that provides the switching functionality of a two-form C
switch.
The Le75181 is designed to provide power ringing access 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 analog line card applications. The Le75181 has three
states: the idle talk state (line break switches closed, ringing access switches open), power ringing state (line break switches
open, ringing access switches closed), and all OFF state.
The Le75181 offers break-before-make or make-before-break switching, with simple logic level input control. Because of the
solid-state construction, voltage transients generated when switching into an inductive ringing load 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 circuitry 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 protection,
to prevent breakdown in the presence of a transient fault condition (i.e., passing the transient on to the ringing generator).
Incorporated into the Le75181A and Le75181C is a diode bridge/SCR clamping circuit, current-limiting circuitry, and a thermal
shutdown mechanism to provide protection to the SLIC device and subsequent circuitry during fault conditions (see block
diagram). 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 thermal shutdown circuits.
The Le75181B version provides only an integrated diode bridge along with current limiting and thermal shutdown, as shown in
the block diagram. This will cause positive faults to be directed to ground and negative faults to battery. In either polarity, faults
are reduced by the current-limit and/or thermal shutdown mechanisms.
The default power up state is in Idle/Talk state unless otherwise being overwritten by external controls.
To protect the Le75181 from an overvoltage fault condition, use of a secondary protector is required. The secondary protector
must limit the voltage seen at the tip/ring terminals to prevent the breakdown voltage of the switches from being exceeded. To
minimize stress on the solid-state contacts, use of a foldback- or crowbar- type secondary protector is recommended. With proper
choice of secondary protection, a line card using the Le75181 will meet all relevant ITU-T, LSSGR, FCC, or UL* protection
requirements.
The Le75181 operates off of a 5-V supply only. This gives the device extremely low idle and active power dissipation and allows
use with virtually any range of battery voltage. This makes the Le75181 especially appropriate for remote power applications
such as DAML or FOC/FITL or other Bellcore TA 909 applications where power dissipation is particularly critical.
A battery voltage is also used by the Le75181, only as a reference for the integrated protection circuit. The Le75181 will enter an
all OFF state upon loss of battery.
During power ringing, to turn on and maintain the ON state, the ring access switch will draw a nominal 2 mA from the ring
generator.
The Le75181ASC/BSC/CSC device is packaged in a 16-pin, plastic SOIC (GULL) package.
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Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
