Le75181
Table 5. Make-Before-Break Operation
INPUT
1
T
SD
1/Float
State
Power
Ringing
Make-
before-
break
Idle/Talk
—
SW4 waiting for next zero current
crossing to turn off, maximum time—one-
half of ringing. In this transition state,
current that is limited to the dc break
switch current-limit value will be sourced
from the ring node of the SLIC.
Zero cross current has occurred.
Timing
Break Switches
1&2
Open
Ring Return
Switch 3
Closed
Data Sheet
Ring Access
Switch 4
Closed
0
1/Float
Closed
Open
Closed
0
1/Float
Closed
Open
Open
Table 6. Break-Before-Make Operation
INPUT
1
1
0
0
T
SD
1/Float
0
0
1/Float
State
Power
Ringing
All Off
All Off
Idle/Talk
—
Hold this state for
≤25
ms. SW4 waiting
for zero current to turn off.
Zero current has occurred and SW4 has
opened. Transition on INPUT should
occur during 25 ms hold.
Release break switch pair.
Timing
Break Switches
1&2
Open
Open
Open
Closed
Ring Return
Switch 3
Closed
Open
Open
Open
Ring Access
Switch 4
Closed
Closed
Open
Open
POWER SUPPLIES
Though both the 5-V and battery supplies are brought onto the Le75181 device, only the 5-V supply is required for switch
operation; that is, state control is powered exclusively off of the 5-V supply. Because of this, the Le75181 device offers extremely
low power dissipation, both in the Idle and Active states.
The battery voltage is not used for switch state control, but rather as a reference voltage by the integrated secondary protection
circuit. When the voltage at TBAT or RBAT drops 2 V to 4 V below the battery, the integrated SCR will trigger, thus preventing
fault-induced overvoltage situations at the TBAT/RBAT nodes.
LOSS OF BATTERY VOLTAGE
As an additional protection feature, the Le75181 device monitors the battery voltage. Upon loss of battery voltage, the Le75181
will automatically enter an all OFF state and remain in that state until the battery voltage is restored. The Le75181 is designed
so that the device will enter the all OFF state if the battery rises above approximately –10 V and will remain off until the battery
drops below approximately –15 V.
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 Le75181 will minimize and possibly eliminate the contribution to the overall system impulse noise that is associated
with ringing access switches. Because of this characteristics of the Le75181, 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.
9
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
