le75183 Zarlink Semiconductor, le75183 Datasheet - Page 15

• Manufacturer Part Number: le75183
• Description: Line Card Access Switch
• Manufacturer: Zarlink Semiconductor

Le75183
Data Sheet
Monitoring the battery for the automatic shutdown feature will draw a small current from the battery, typically 4 µA. This will add
slightly to the overall power dissipation of the device.
IMPULSE NOISE
Using the Le75183 will minimize and possibly eliminate the contribution to the overall system impulse noise that is associated
with ringing access switches. Because of this characteristic of the Le75183 device, it may not be necessary to incorporate a zero
cross switching scheme. This ultimately depends upon the characteristics of the individual system and is best evaluated at the
board level.
PROTECTION
Integrated SLIC Device Protection
Diode Bridge/SCR
In the Le75183A and the Le75183C versions, protection 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
Le75183B and the Le75183D versions, 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.
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 negative 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 battery 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 integrated protection circuit
and subsequent circuitry is limited 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.
During a power cross event, the current that is passed through the break switches and presented to the integrated protection
circuit and subsequent circuitry is limited 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 negative temperature 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 temperature shutdown mechanism will activate and the device will enter an all off mode.
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Zarlink Semiconductor Inc.