Data Sheet
November 1999
L7581 Ringing Access Switch
states: the idle talk state (line break switches closed,
ringing access switches open), the power ringing
state (line break switches open, ringing access
switches closed), and an all OFF state.
Features
■ Small size/surface-mount packaging
■ Monolithic IC reliability
The L7581 offers break-before-make or make-before-
break switching, with simple logic level input control.
Because of the solid-state construction, voltage tran-
sients generated when switching into an inductive
ringing load during ring cadence or ring trip are mini-
mized, possibly eliminating the need for external zero
cross switching circuitry. State control is via logic
level inputs, so no additional driver circuitry is
required.
■ Low impulse noise
■ Make-before-break, break-before-make operation
■ Clean, bounce-free switching
■ Low, matched ON-resistance
■ Built-in current limiting, thermal shutdown, and
SLIC protection
■ 5 V only operation, very low power consumption
■ Battery monitor, all OFF state upon loss of battery
■ No EMI
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).
■ Latched logic level inputs, no drive circuitry
■ Only one external protector required
Incorporated into the L7581Axx 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 Figure 1). 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.
Applications
■ Central office
■ DLC
■ PBX
■ DAML
■ HFC/FITL
The L7581Bxx version provides only an integrated
diode bridge along with current limiting and thermal
shutdown, as shown in Figure 2. This will cause pos-
itive 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 mecha-
nisms.
Description
The L7581 Ringing Access Switch is a monolithic
solid-state device that provides the switching func-
tionality of a 2 form C switch.
The L7581 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 ana-
log line card applications. The L7581 has three