Data Sheet
September 2001
Full-Feature SLIC and Ringing Relay for TR-57 Applications
L9313 Line Interface and Line Access Circuit
Agere Systems Inc.
29
Supervision
Loop Closure
Loop closure supervision threshold is programmed via
an applied voltage source or ground, through a resistor
at the LCTH input. Loop closure status is presented at
the NSTAT output. NSTAT is an unlatched output that
represents either the loop closure or ring trip status,
depending on the device state. See Table 2 for more
details. Loop closure threshold current (I
LCTH
) is set by:
= I
LCTH
(mA)
where:
R
LCTH
is a resistor from the LCTH node to ground or a
voltage source.
V
LCTH
is ground or an external voltage source.
There is a built-in hysteresis associated with the loop
closure detector. The above equation describes the on-
hook to off-hook threshold. To help prevent false
glitches, the off-hook to on-hook threshold will be a typ-
ical 20% lower than the corresponding on-hook to off-
hook threshold.
Ring Trip
Ring trip is set by the value of RS1.
The ring trip threshold at the ring trip inputs is
±2.5 V
minimum, ±3.5 V maximum.
A resistor value of 400
, as shown in Figure 4, will set
the ring trip current threshold to ±7.5 mA typical.
Ring trip is asserted upon entering the ringing mode
until the second zero crossing of ringing. This is either
a positive-going zero crossing (between –40 V and
–30 V at –50 V V
BAT
) or a negative-going zero crossing
(between –10 V and –20 V at –50 V V
BAT
). The different
threshold for positive-going and negative-going zero
crossings is the result of hysteresis of approximately
20 V. The act of turning on the switch may or may not
produce a ringing zero crossing, therefore, there may
be a delay of up to almost one cycle of ringing or 50 ms
until NSTAT is high.
Ring trip will not be asserted unless the ring trip thresh-
old is exceeded for two zero crossings. This is either a
positive-going zero crossing (between –40 V and –30 V
at –50 V V
BAT
) or a negative-going zero crossing
(between –10 V and –20 V at –50 V V
BAT
). The different
threshold for positive-going and negative-going zero
crossings is the result of hysteresis of approximately
20 V.
Note that since the ringing voltage is monitored at
RSW, one zero crossing can occur at switch turn-on
depending on initial conditions.
Ring trip is asserted immediately if the ring trip input is
15 V ± 3 V.
Ring Ground Detector
In the ground start application, a common-mode cur-
rent detector is used to indicate that an off-hook has
occurred. The detection threshold is set by connecting
a resistor from ICM to ground.
2350/R
ICM
(k
) = I
TH
(mA)
Additionally, a filter capacitor across R
ICM
will set the
time constant of the detector. No hysteresis is associ-
ated with this detector.
Switching Behavior
The solid-state ring relay in the L9313 device is able to
provide either make-before-break or break-before-
make timing with respect to switching into and out of
the ring mode. If switching is done directly into and out
of the ring mode, the design of the L9313 will give
make-before-break switching with respect to both the
ring and tip side switches. To achieve break-before-
make switching, the user should via software control
enter an intermediate all-off mode when switching into
and out of the ring mode. The all-off state should be
held a minimum of 8 ms.
Make-Before-Break Operation
The break switches are constructed from DMOS tran-
sistors. The tip side ring return is also a DMOS transis-
tor. Because the on resistance of the break switches is
less than the tip side ring return switch, the break
switches are physically bigger. This implies a larger
gate to source capacitance, with inherently slower
switching speeds since it will take longer to charge or
discharge the gate to source capacitance of the break
switches (to change the state of the switch). The ring
access switch is a pnpn type device. The pnpn device
has inherently faster switching speeds than any of the
DMOS type switches.
Going from the active to ring mode, the smaller tip side
ring return switch and the pnpn ring access switch will
change states before the larger break switches. Thus,
the ring contacts are made before the line break
switches are broken: make-before-break operation.
Going from the ring mode to active or scan, the natural
tendency is for the smaller tip side ring return DMOS to
break or open, before the larger DMOS can turn on.
This would not be make-before-break operation on the
tip side. Thus, circuitry is added to speed up charging
of the tip break switch, to speed up the turn on of that
switch to give make-before-break operation on the tip
side.
REF
R
LCTH
k
V
LCTH
)
–
(
)
100 V