Data Sheet
July 2001
Ringing Relay, and GR-909 Test Access
L9311 Full-Feature SLIC with High Longitudinal Balance,
32
Agere Systems Inc.
Applications
(continued)
dc Characteristics
(continued)
Battery Feed
The L9311 operates in a dc unbalanced mode. In the
forward active state, under open circuit (on-hook) con-
ditions, with the default overhead chosen, the tip to ring
voltage will be a nominal 5.5 V less than the battery.
This is the overhead voltage. The tip and ring overhead
is achieved by biasing ring a nominal 3.5 V above bat-
tery and by biasing tip a nominal 2.0 V below ground.
During off-hook conditions, some dc resistance will be
applied to the subscriber loop as a function of the phys-
ical loop length, protection, and telephone handset. As
the dc resistance decreases from infinity (on-hook) to
some finite value (off-hook), the tip to ring voltage will
decrease as shown in Figure 13.
12-3431a (F)
Figure 13. Tip/Ring Voltage
As illustrated in Figure 13, as loop length decreases,
the tip to ground voltage will decrease with a slope cor-
responding to one-half the internal dc feed resistance
of the SLIC (typical 75
). The ring to ground voltage
will also decrease with a slope corresponding to one-
half the internal dc feed resistance of the SLIC, until the
SLIC reaches the current-limit region of operation. At
that point, the slope of the ring to ground voltage will
increase to the sum of one half the internal dc feed
resistance plus approximately 10 k
.
The dc feed characteristic can be described by:
I
LOOP
=
V
T/R
=
where:
I
LOOP
= dc loop current.
V
T/R
= dc loop voltage.
V
BAT
= battery voltage magnitude.
V
OH
= overhead voltage.
R
LOOP
= loop resistance, including wire and handset
resistance.
R
P
= protection resistance.
R
dc
= SLIC internal dc feed resistance.
12-3050.g (F)
Notes:
V
BAT1
= –48 V.
V
BAT2
= –24 V.
I
LIM
= 40 mA (R
PROG
= 66.5 k
).
Figure 14. L9311 Loop Current vs. Loop Voltage
VTIP TO GND
(1/2)R
dc
BEGIN CURRENT LIMITING
(1/2)R
dc
(1/2)R
dc
+ R
LIM
DECREASING LOOP LENGTH
V
BAT
VRING TO GND
BAT
V
OH
–
R
LOOP
2R
P
R
dc
+
+
----------V
BAT
R
LOOP
V
OH
2R
P
+
–
----V
)
R
LOOP
R
dc
+
L
0
5
10
25
0
20
30
40
50
LOOP VOLTAGE (V)
15
20
10
1
R
dc
30
45
35
40
1
10 k