le75282 Zarlink Semiconductor, le75282 Datasheet - Page 10

• Manufacturer Part Number: le75282
• Description: Dual Intelligent Line Card Access Switch
• Manufacturer: Zarlink Semiconductor

POWER SUPPLIES
Both the VDD and battery supply are brought onto the Le75282 device. The Le75282 device requires only the VDD supply for
switch operation; that is, state control is powered exclusively off of the VDD supply. Because of this, the Le75282 device offers
extremely low power dissipation, both in the idle and active states.
LOSS OF BATTERY VOLTAGE
As an additional protection feature, the Le75282 device monitors the battery voltage. Upon loss of battery voltage, both channels
of the Le75282 device will automatically enter an All Off state and remain in that state until the battery voltage is restored. The
Le75282 device is designed such that the device will enter the All Off state if the battery rises above –12 V (typ.) and will remain
off until the battery drops below –14 V (typ.).
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 Le75282 device 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 Le75282 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.
INTEGRATED SLIC DEVICE PROTECTION
Diode Bridge
Le75282 device 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.
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. Negative lightning is directed to battery via steering diodes in the diode bridge.
For power cross and power induction faults, the positive cycle of the fault is clamped a diode drop above ground and fault currents
are steered to ground. The negative cycle of the power cross is steered to battery. Fault currents are limited by the current-limit
circuit.
Current Limiting
During a lightning event, the current that is passed through the Le75282 device is limited by the dynamic current-limit response
of the break switches (assuming Idle/Talk state). When the voltage seen at the ALINEx/BLINEx 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 ASLICx/
BSLICx 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 Le75282 is limited by the dc current-limit response of the break
switches (assuming Idle/Talk state). The DC current limit is dependent on the switch differential voltage, as shown in
page
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 ASLICx/BSLICx 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 state.
12.
Table 8. Break-Before-Make Operation
CFG=0, RD3=0
RD2
1
X
X
0
RD1
X
X
0
0
OFFx
1
0
0
1
Idle/Talk
Ringing
All Off
All Off
State
—
Hold this state for 25 ms. SW4
waiting for zero current to turn off.
Zero current has occurred and
SW4 has opened.
Release break switches.
Zarlink Semiconductor Inc.
Timing
10
Switches
1x & 2x
Break
OFF
OFF
OFF
ON
Ringing
Return
Switch
OFF
OFF
OFF
ON
3x
Ringing
Access
Switch
OFF
OFF
ON
ON
4x
Figure 2, on
Switches
Access
5x & 6x
Test
OFF
OFF
OFF
OFF