Data Sheet
November 1999
L7582 Tip Ring Access Switch
Switching Behavior
(continued)
Table 11. Break-Before-Make Operation
ACCESS INPUT
0V
5V
5V
5V
T
SD
Float
State
Timing
Break
Switches
1&2
Open
Open
Ring
Return
Switch 3
Closed
Open
Ring
Access
Switch 4
Closed
Closed
Line Access
Switches
5&6
Open
Open
5V
0V
5V
0V
Power
—
Ringing
Float All Off Hold this state for
≤25
ms.
SW4 waiting for zero cur-
rent to turn off.
Float All Off Zero current has occurred
and SW4 has opened.
Float Idle/Talk Release break switches.
Open
Closed
Open
Open
Open
Open
Open
Open
Notes:
Break-before-make operation can also be achieved using T
SD
as an input. In lines two and three of Table 11, instead of using the logic input pins
to force the all OFF state, force T
SD
to ground. This will override the logic inputs and also force the all OFF state. Hold this state for 25 ms. Dur-
ing this 25 ms all OFF state, toggle the inputs from 10 (ringing state) to 00 (idle/talk state). After 25 ms, release T
SD
to return switch control to
the input pins which will set the idle talk state.
When using the L7582 in this mode, forcing T
SD
to ground will override the INPUT pins and force an all OFF state. Setting T
SD
to 5 V will allow
switch control via the logic INPUT pins. However, setting T
SD
to 5 V will also disable the thermal shutdown mechanism. This is not recom-
mended. Therefore, to allow switch control via the logic INPUT pins, allow T
SD
to float.
Thus, when using T
SD
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 T
SD
operation in L7582 is different than T
SD
operation of the L7581, where application of 5 V does not disable the thermal shut-
down mechanism.
Power Supplies
Both the 5 V and battery supply are brought onto the
L7582. The L7582 requires only the 5 V supply for
switch operation; that is, state control is powered exclu-
sively off of the 5 V supply. Because of this, the L7582
offers extremely low power dissipation, both in the idle
and active states.
The battery voltage is not used for switch state control.
The battery is used as a reference voltage by the
integrated secondary protection circuit. When the volt-
age at T
BAT
or R
BAT
drops 2 V to 4 V below the battery,
the integrated SCR will trigger, thus preventing
fault-induced overvoltage situations at the T
BAT
/R
BAT
nodes.
The L7582 is designed such that the device will enter
the all OFF state if the battery rises above –10 V and
will remain off until the battery drops below –15 V.
Monitoring the battery for the automatic shutdown fea-
ture will draw a small current from the battery, typically
4
µA.
This will add slightly to the overall power dissipa-
tion of the device.
Impulse Noise
Using the L7582 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 L7582, it may not
be necessary to incorporate a zero cross switching
scheme. This ultimately depends upon the characteris-
tics of the individual system and is best evaluated at
the board level.
Loss of Battery Voltage
As an additional protection feature, the L7582 monitors
the battery voltage. Upon loss of battery voltage, the
L7582 will automatically enter an all OFF state and
remain in that state until the battery voltage is restored.
Lucent Technologies Inc.
9
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