Data Sheet
November 1999
L7582 Tip Ring Access Switch
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.
Protection
Integrated SLIC Protection
Diode Bridge/SCR
In the L7582Axx version, protection to the SLIC device
or other subsequent circuitry is provided by a combina-
tion of current-limited break switches, a diode bridge/
SCR clamping circuit, and a thermal shutdown mecha-
nism. In the L7582Bxx version, protection to the SLIC
device or other subsequent circuitry is provided by a
combination of current-limited break switches, a diode
bridge, and a thermal shutdown mechanism.
Note that the current-limit circuitry has a negative tem-
perature coefficient. Thus, if the device is subjected to
an extended power cross, the value of current seen at
TBAT/RBAT will decrease as the device heats due to the
fault current. If sufficient heating occurs, the tempera-
ture shutdown mechanism will activate and the device
will enter an all off mode.
In both 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.
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 TSD, when used as an output,
will read 0 V when the device is in the thermal shut-
down mode and +VDD during normal operation.
Note that for the SCR to foldback or crowbar, the ON
voltage (see Table 11) 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.
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 TBAT/RBAT 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.
In the B version, negative lightning is directed to battery
via steering diodes in the diode bridge.
For power cross and power induction faults, in both ver-
sions, the positive cycle of the fault is clamped a diode
drop above ground and fault currents are steered to
ground. In the A version, the negative cycle will cause
the SCR to trigger when the voltage exceeds the bat-
tery reference voltage by 2 V to 4 V. When the SCR
triggers, fault current is steered to ground. In the B ver-
sion, the negative cycle of the power cross is steered to
battery.
If the magnitude of power is great enough, the external
secondary protector could trigger, thereby shunting all
current to ground.
Current Limiting
In the L7582, the thermal shutdown mechanism can be
disabled by forcing the TSD pin to +VDD. This functional-
ity differs from the L7581, whose thermal shutdown
mechanism cannot be disabled.
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 TLINE/RLINE 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 TBAT/RBAT nodes will typically be a pulse of
magnitude 2.5 A and duration less than 0.5 µs.
10
Lucent Technologies Inc.
AGERE [ AGERE SYSTEMS ]
