LUCL9310AP-D AGERE [Agere Systems], LUCL9310AP-D Datasheet - Page 40

• Manufacturer Part Number: LUCL9310AP-D
• Description: Line Interface and Line Access Circuit Full-Feature SLIC,Ringing Relay,and Test Access Device
• Manufacturer: AGERE [Agere Systems]

Full-Feature SLIC, Ringing Relay, and Test Access Device
Protection
External Protection
The overall device protection is achieved through a
combination of the external overvoltage and overcur-
rent devices, along with the integrated thermal shut-
down feature, the integrated window comparator,
the break switch foldback characteristic, and the
dc/dynamic current-limit response of the break and tip
return switches.
Active Mode Response at PT/PR
The line break switches and tip return switch are cur-
rent-limited switches. The current-limit mechanism lim-
its current through the switch to the specified dc current
limit under low frequency or dc faults (power cross
and/or tip-ring to ground short) and limits the current to
the specified dynamic current-limit response under
transient faults, such as lightning.
During a lightning fault (typical 1000 V 10 x 700 s
applied surge), the current-limited line break switches
will pass typically 2.5 A for 0.5 s before forcing the
break switches off. Once in the off state, the external
protection device must ensure that the off-state voltage
rating of 320 V is not exceeded. Note that the maxi-
mum differential voltage is the positive zener rating of
the protection device less the battery voltage, which
will appear on the line feed side of the switch.
For a lower-voltage power cross, whose maximum
peak voltage is below the foldback voltage breakpoint 1
(V1), the current-limited break switch will pass the cur-
rent equal to the dc current limit. The current limit has a
negative temperate coefficient, so as the device contin-
ues to pass current, the current limit will reduce with
increasing device temperature. Ultimately, the device
will reach the thermal shutdown temperature and the
thermal shutdown mechanism will force an all-off state,
which will stop current flow and begin device cooling. In
the all-off state, the external protection device ensures
that the switch off-state voltage rating is not exceeded.
Once the device cools significantly, the break switches
will turn on, and current will begin to flow again, until
temperature forces the all-off state. This will continue
until the fault condition is gone.
Sneak-under surge is a voltage surge that is just below
the clamping threshold of the secondary protection
device. For this type of surge, when the surge voltage
40
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(continued)
is below the foldback voltage breakpoint 1, operation is
as described above. When the surge voltage rises
above the foldback voltage breakpoint 1 (V1), but is still
less than the secondary protector clamping voltage, the
line break switch will crowbar into the high-impedance
region of its I-V characteristic and reduce current to the
specified I
For surges whose magnitude range above the trigger
of the external secondary protector, the device will
operate as described above for the portion of the surge
below the secondary protector trigger voltage. When
the voltage rises above the external secondary protec-
tor’s trigger voltage, the secondary protector will crow-
bar on, shunting fault current to ground and reducing
the tip/ring voltage seen at the device.
In the active mode, the external secondary protector
must ensure that the off-state voltage ratings of the ring
access and ring return switch are not exceeded. Nor-
mally, the ring return switch is connected to ground on
the TRING side and to the protector on the PT side;
thus, the protector on the tip side in the active mode
must clamp at less than 320 V. As will be seen in the
Ring Mode Response at PT/PR section, during the
power ringing mode, this clamp voltage on the tip side
is significantly less than 320 V.
Normally, the ring access switch is connected to the
ring generator on the RRING side and to the protector
on the PR side; thus, on one side of the switch, there is
the battery voltage and the peak negative ring signal,
and on the PR side, the maximum turn-on voltage of
the secondary protector. The ring access switch is of
pnpn construction. Thus, if the off-state voltage rating
of the ring access switch is exceeded, the device will
crowbar into a low-impedance state. This will cause a
surge into the ring generator and can cause the on-
state current rating of the switch to be exceeded.
The difference of the battery plus peak negative ring
signal voltage less the maximum turn on of the second-
ary protector must not exceed the off-state voltage rat-
ing of the ring access switch. Additionally, as the
secondary protector will see the power ring signal, the
minimum turn-on rating of the secondary protector
must be high enough to not clamp the ring signal and
cause clipping distortion. The ring side will see the full
power ring voltage, and the tip side switch will see the
power ringing voltage that is attenuated by the ringing
load, subscriber loop, feed resistor, and protection
resistors; thus, the ring side secondary protector
requires a higher clamping voltage than the tip side.
LIMIT
2 value.
Agere Systems Inc.
July 2001