Data Sheet
L7583A/B/C/D Line Card Access Switch
Switching Behavior
February 2001
switch is waiting for the next zero current cross, so it
can close. During this interval, current that is limited to
the dc break switch current-limit value will be source
from the ring node of the SLIC.
When switching from the power ringing state to the
idle/talk state, via simple logic level input control, the
L7583 is able to provide control with respect to the tim-
ing when the ringing access contacts are released rela-
tive to the state of the line break contacts.
This current is presented to the internal protection cir-
cuit. If the SCR-type protector is used (A or C codes), if
by random probability the ring-to-idle transition occurs
during a portion of the ring cycle when the ringing volt-
age exceeds the protection circuit SCR turn-on volt-
age, and if current in excess of the SCR’s turn-on
current is also available, the SCR may turn on. Once
the SCR is triggered on, if the SLIC is capable of sup-
plying current in excess of the holding current, the SCR
may be latched on by the SLIC.
Make-before-break operation occurs when the line
break switch contacts are closed (or made) before the
ringing access switch contact is opened (or broken).
Break-before-make operation occurs when the ringing
access contact is opened before the line break switch
contacts are closed.
Using the logic level input pins RING, TESTin, and
TESTout, either make-before-break or break-before-
make operation of the L7583 is easily achieved. The
logic sequences for either mode of operation are given
in Table 13 and Table 14. See the Truth Tables (Table
16 and Table 17) for an explanation of logic states.
The probability of this event depends on the character-
istics of the given SLIC and of the holding current of the
L7583 A or C device. The SCR hold current distribution
is designed to be safely away from the test limit of
80 mA. The higher the distribution, the lower the proba-
bility of the latch.
When using an L758X in the make-before-break mode,
during the ring-to-idle transition, for a period of up to
one-half the ringing frequency, the ring break switch
and the pnpn-type ring access switch can both be in
the ON state. This is the maximum time after the logic
signal at INRING has transitioned that the ring access
If this situation is of concern for a given board design,
either use the A or C series device in the break-before-
make mode (eliminates the original 25 ms current
pulse) or use a B or D series device (eliminates the
SCR).
Table 13. Make-Before-Break Operation
Break
Ring
Ring
All Other
RING TESTin TESTout
TSD
State
Timing
—
Switches Return Access Access
3 & 4
Switch 7 Switch 8 Switches
5 V
0 V
0 V
0 V
0 V
0 V
Float Power
Ringing
Open
Closed
Closed
Open
Float Make-
SW8 waiting for next
Closed
Open
Closed
Open
before- zero current crossing
break
to turn off maximum
time—one-half of
ringing. In this transi-
tion state, current
that is limited to the
dc break switch cur-
rent-limit value will be
sourced from the ring
node of the SLIC.
0 V
0 V
0 V
Float Idle/Talk Zero cross current
has occurred.
Closed
Open
Open
Open
10
Lucent Technologies Inc.
AGERE [ AGERE SYSTEMS ]
