le75183 Zarlink Semiconductor, le75183 Datasheet - Page 14

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

Notes:
Break-before-make operation can be achieved using TSD as an input. In lines two and three of Table 10, instead of using the logic input pins to
force the all OFF state, force TSD to logic 0. This will override the logic inputs and also force the all OFF state. Hold this state for 25 ms. During
this 25 ms all OFF state, toggle the inputs from 10 (ringing state) to 00 (idle/talk state). After 25 ms, release TSD to return switch control to the
input pins which will set the idle talk state.
When using the Le75183A/B/C/D in this mode, forcing TSD to logic 0 will override the INPUT pins and force an all OFF state. Setting TSD to logic
1 will allow switch control via the logic INPUT pins. However, setting TSD to logic 1 will also disable the thermal shutdown mechanism. This is
not recommended. Therefore, to allow switch control via the logic INPUT pins, allow TSD to float.
Thus, when using TSD as an input, the two recommended states are 0 (overrides logic input pins and forces all OFF state) and float (allows switch
control via logic input pins and thermal shutdown mechanism is active). This may require use of an open-collector buffer.
Also note that TSD operation in Le75183 is different than TSD operation of the L75181, where application of logic 1 does not disable the thermal
shutdown mechanism.
POWER SUPPLIES
Though both the 5-V and battery supplies are brought onto the Le75183 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 Le75183 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 Le75183 device monitors the battery voltage. Upon loss of battery voltage, the Le75183
will automatically enter an all OFF state and remain in that state until the battery voltage is restored. The Le75183 is designed so
that the device will enter the all OFF state if the battery rises above typically –10 V and will remain off until the battery drops below
typically –15 V.
IN
IN
RING
RING
1
1
1
0
1
0
0
Table 9. Make-Before-Break Operation
Table 10. Break-Before-Make Operation
IN
IN
TESTin
TESTin
0
0
0
0
0
0
0
IN
IN
TESTout
TESTout
0
1
1
0
0
0
0
1/Float
1/Float
1/Float
1/Float
T
1/Float
1/Float
1/Float
SD
T
SD
Power
Ringing
All Off
All Off
Idle/Talk
State
Power
Ringing
Make-
before-
break
Idle/Talk
State
Zarlink Semiconductor Inc.
—
Hold this state for
≤
zero current to turn off.
Zero current has occurred
and SW8 has opened.
Release break switches.
25 ms. SW8 waiting for
—
SW8 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.
14
Timing
Timing
Switches
Closed
Break
Switches
3 & 4
Open
Open
Open
Closed
Closed
Break
Open
3 & 4
Switch 7
Return
Closed
Switch 7
Open
Open
Open
Ring
Return
Closed
Open
Open
Ring
Switch 8
Access
Switch 8
Closed
Closed
Access
Closed
Closed
Open
Open
Ring
Open
Ring
Switches
All Other
Switches
All Other
Access
Open
Open
Open
Open
Open
Open
Open