L8583D Line Card Access Switch
Data Sheet
October 2002
Switching Behavior
(continued)
Table 14. Break-Before-Make Operation—Part II
INPUT TESTin TESTout T
SD
State
Timing
Break
Ring
Ring
All Other
Switches Return Access Switches
3 and 4 Switch 7 Switch 8
Open
Closed
Closed
Open
Open
Open
Closed
Open
5V
5V
0V
0V
0V
5V
5V
0V
0V
0V
5V
0V
Power
—
Ringing
Float All Off Hold this state for
≤25
ms. SW8
waiting for zero current to turn
off.
Float All Off Zero current has occurred and
SW8 has opened.
Float
Idle/Talk Release break switches.
Float
Open
Closed
Open
Open
Open
Open
Open
Open
Notes:
Break-before-make operation can be achieved using T
SD
as an input. In lines two and three of Table 14, 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. During this
25 ms all-off state, toggle the inputs from 100 (ringing state) to 000 (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 L8583D 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 L8583D 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 L8583D. The L8583D requires only the 5 V supply for switch
operation; that is, state control is powered exclusively off of the 5 V supply. Because of this, the L8583D offers
extremely low power dissipation, both in the idle and active states. The battery voltage is not used for switch state
control and is only used by the battery monitor circuit.
Loss of Battery Voltage
As an additional protection feature, the L8583D monitors the battery voltage. Upon loss of battery voltage, the
L8583D will automatically enter an all-off state and remain in that state until the battery voltage is restored. The
L8583D 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 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 L8583D 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 L8583D, it may not be necessary to
incorporate a zero cross switching scheme. This ultimately depends upon the characteristics of the individual sys-
tem and is best evaluated at the board level.
12
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