L7583A/B/C/D Line Card Access Switch
Data Sheet
February 2001
During a power cross event, the current that is passed
through the break switches and presented to the inte-
grated protection circuit and subsequent circuitry is lim-
ited by the dc current-limit response of the break
switches (assuming idle/talk state). The dc current limit
is specified over temperature between 100 mA and
250 mA. Note that the current-limit circuitry has a nega-
tive temperature coefficient. Thus, if the device is sub-
jected to an extended power cross, the value of current
seen at T
BAT
/R
BAT
will decrease as the device heats
due to the fault current. If sufficient heating occurs, the
temperature shutdown mechanism will activate and the
device will enter an all off mode.
Temperature Shutdown Mechanism
When the device temperature reaches a minimum of
110 °C, the thermal shutdown mechanism will activate
and force the device into an all OFF state, regardless
of the logic input pins. Pin T
SD
, when used as an out-
put, will read 0 V when the device is in the thermal
shutdown mode and +V
DD
during normal operation.
During a lightning event, due to the relatively short
duration, the thermal shutdown will not typically acti-
vate.
During an extended power cross, the device tempera-
ture will rise and cause the device to enter the thermal
shutdown mode. This forces an all off mode, and the
current seen at T
BAT
/R
BAT
drops to zero. Once in the
thermal shutdown mode, the device will cool and exit
the thermal shutdown mode, thus reentering the state it
was in prior to thermal shutdown. Current, limited to the
dc current-limit value, will again begin to flow and
device heating will begin again. This cycle of entering
and exiting thermal shutdown will last as long as the
power cross fault is present. The frequency of entering
and exiting thermal shutdown will depend on the mag-
nitude of the power cross. If the magnitude of the
power cross is great enough, the external secondary
protector may trigger shunting all current to ground.
In the L7583, the thermal shutdown mechanism can be
disabled by forcing the T
SD
pin to +V
DD
. This functional-
ity is different from the L7581, whose thermal shutdown
mechanism cannot be disabled.
Electrical specifications relating to the integrated over-
voltage clamping circuit are outlined in Table 15.
Protection
Integrated SLIC Protection
Diode Bridge/SCR
In the L7583Axx and the L7583Cxx versions, protec-
tion to the SLIC device or other subsequent circuitry is
provided by a combination of current-limited break
switches, a diode bridge/SCR clamping circuit, and a
thermal shutdown mechanism. In the L7583Bxx and
the L7583Dxx versions, protection to the SLIC device
or other subsequent circuitry is provided by a combina-
tion of current-limited break switches, a diode bridge,
and a thermal shutdown mechanism.
In both protection versions, during a positive lightning
event, fault current is directed to ground via steering
diodes in the diode bridge. Voltage is clamped to a
diode drop above ground. In the A version, negative
lightning causes the SCR to conduct when the voltage
goes 2 V to 4 V more negative than the battery. Fault
currents are then directed to ground via the SCR and
steering diodes in the diode bridge.
Note that for the SCR to foldback or crowbar, the ON
voltage (see Table 14) of the SCR must be less nega-
tive than the battery reference voltage. If the battery
voltage is less negative than the SCR ON voltage, the
SCR will conduct fault currents to ground; however, it
will not crowbar.
In the B/D version, negative lightning is directed to bat-
tery via steering diodes in the diode bridge.
For power cross and power induction faults, in both
protection versions, the positive cycle of the fault is
clamped a diode drop above ground and fault currents
steered to ground. In the A/C version, the negative
cycle will cause the SCR to trigger when the voltage
exceeds the battery reference voltage by 2 V to 4 V.
When the SCR triggers, fault current is steered to
ground. In the B/D version, the negative cycle of the
power cross is steered to battery.
Current Limiting
During a lightning event, the current that is passed
through the break switches and presented to the inte-
grated protection circuit and subsequent circuitry is lim-
ited by the dynamic current-limit response of the break
switches (assuming idle/talk state). When the voltage
seen at the T
LINE
/R
LINE
nodes is properly clamped by
an external secondary protector, upon application of a
1000 V, 10 x 1000 pulse (LSSGR lightning), the current
seen at the T
BAT
/R
BAT
nodes will typically be a pulse of
magnitude 2.5 A and duration less than 0.5 µs.
12
Lucent Technologies Inc.
AGERE [ AGERE SYSTEMS ]
