Lucent Technologies Inc.
23
Data Sheet
April 2000
L8560 Low-Power SLIC with Ringing
Applications
(continued)
dc Applications
(continued)
12-2563.c (F)
Figure 23. SLIC 2-Wire Output Stage
In addition to the required peak signal level, the SLIC
needs about 2 V from each power supply to bias the
amplifier circuitry. It can be thought of as an internal
saturation voltage. Combining the saturation voltage
and the peak signal level, the required overhead can
be expressed as:
x 10
dBm/20
where V
SAT
is the combined internal saturation voltage
between the tip/ring amplifiers and V
BAT
(4.0 V typ.). R
P
(
) is the protection resistor value. Z
T/R
(
) is the ac
loop impedance.
Example 1, On-Hook Transmission of a Meter
Pulse:
Signal level: 2.2 Vrms into 200
35
protection resistors
I
LOOP
= 0 (on-hook transmission of the metering signal)
V
OH
= 4.0 +
(2.2)
= 8.2 V
Accounting for V
SAT
tolerance of 0.5 V, a nominal over-
head of 8.7 V would ensure transmission of an undis-
torted 2.2 V metering signal.
Adjusting Overhead Voltage
To adjust the open loop 2-wire voltage, pin DCR
(44-pin PLCC only) is programmed at the midpoint of a
resistive divider from ground to either –5 V or V
BAT
. In
the case of –5 V, the overhead voltage will be indepen-
dent of the battery voltage. Figure 24 shows the equiv-
alent input circuit to adjust the overhead.
12-2562.b (F)
Figure 24. Equivalent Circuit for Adjusting the
Overhead Voltage
The overhead voltage is programmed by using the fol-
lowing equation:
V
OH
= 7.1 – 18.18 V
DCR
= 7.1 – 18.18
Adjusting dc Feed Resistance
The dc feed resistance may be adjusted with the help
of Figure 25.
12-2560.c (F)
Figure 25. Equivalent Circuit for Adjusting the dc
Feed Resistance
R
dc
= 55
+ 705
= 55
+ 705
–
V
T/R
[Z
T/R
]
V
AMP
–
+
R
P
R
P
+
V
OH
V
SAT
1
Z
T/R
-----------
+
V
T/R
+
=
Λ
V
SAT
1
Z
T/R
-----------
+
1000
--------------
+
=
1
----------------
200
+
2
DCR
R
1
R
2
–5 V
5
–
+
R
2
R
1
---------------------
×
DCR
R
1
R
3
DCOUT
44-PIN PLCC
DCR
V
DCOUT
--------V
+
R
3
R
1
---------------------