Le75183
12.0
Impulse Noise
Data Sheet
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.
13.0
13.1
13.1.1
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 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.
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 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 version, the negative cycle of the power cross is steered to battery.
13.1.2
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.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
