Data Sheet
November 1999
L7582 Tip Ring Access Switch
The SCR may turn on if:
Switching Behavior (continued)
■ The SCR-type protector is used (A code)
When using an L7582 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
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 sourced
from the ring node of the SLIC.
■ By random probability the ring-to-idle transition
occurs during a portion of the ring cycle when the
ringing voltage exceeds the protection circuit SCR
turn-on voltage.
■ Current in excess of the SCR’s turn-on current is also
available.
Once the SCR is triggered on, if the SLIC is capable of
supplying current in excess of the holding current, the
SCR may be latched on by the SLIC.
This current is presented to the internal protection cir-
cuit.
The probability of this event depends on the character-
istics of the given SLIC and of the holding current of the
L7582A 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.
If this situation is of concern for a given board design,
either use the A series device in the break-before-make
mode (eliminates the original 25 ms current pulse) or
use a B series device (eliminates the SCR).
Table 10. Make-Before-Break Operation
Ring
Ring
Line
Break
Switches
1 & 2
Return Access Access
Switch Switch Switches
ACCESS INPUT TSD
State
Timing
3
4
5 & 6
0 V
0 V
5 V Float Power Ringing
—
Open
Closed Closed
Open Closed
Open
Open
0 V Float Make-before- SW4 waiting for next zero
Closed
break
current crossing to turn off
maximum time—one-half of
ringing. In this transition
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 Float
Idle/Talk
Zero cross current has
occurred.
Closed
Open
Open
Open
8
Lucent Technologies Inc.
AGERE [ AGERE SYSTEMS ]
