34
Lucent Technologies Inc.
Data Sheet
August 1999
People’s Republic of China Applications
L8567 SLIC for
dc Characteristics
(continued)
Loop Range
The following equation is used to determine the dc loop
range.
Where:
R
L
= dc loop range.
|V
BAT
| = magnitude of battery voltage.
V
OH
= SLIC overhead voltage.
I
L
= dc loop current.
R
P
= series protection resistor and resistance of L758X
solid-state switch (if used).
R
dc
= SLIC dc feed resistance.
Example 1, Standard Loop:
Calculate loop range with battery voltage of 48 V, SLIC
maximum overhead of 7.8 V, SLIC dc feed resistance of
65
, 18 mA loop current requirement, worst-case
resistance of L758X switch of 28
, and 50
protec-
tion resistor with worst-case 10% tolerance of 55
.
R
L
= 1937
> 1800
Example 2, Extended Loop:
With a –65 V battery voltage, assuming a SLIC nominal
overhead of 7.1 V, SLIC dc feed resistance of 110
,
18 mA loop current requirement, worst-case resistance
of L758X switch of 28
, and 50
protection resistor
with worst-case 10% tolerance of 55
, what is the
maximum loop length
dc Applications
On-Hook Transmission
In order to drive an on-hook ac signal, the SLIC must
set up the tip and ring voltage to a value less than the
battery voltage. The amount that the open loop voltage
is decreased relative to the battery is referred to as the
overhead voltage. Expressed as an equation,
V
OH
= |V
BAT
| – (V
PT
– V
PR
)
Without this buffer voltage, amplifier saturation will
occur and the signal will be clipped. The L8567 is auto-
matically set at the factory to allow undistorted on-hook
transmission of a 3.17 dBm signal into a 900
ac loop
impedance.
The drive amplifiers are capable of 4 Vrms minimum
(V
AMP
). So, the maximum signal the device can guaran-
tee is:
=
The peak voltage at output of tip and ring amplifiers is
related to the peak signal voltage by:
12-2563 (F)
Figure 27. SLIC 2-Wire Output Stage
R
L
BAT
V
V
OH
–
I
L
2R
P
–
R
dc
–
=
R
L
48 V
7.8 V
–
0.018 A
2
55
28
+
(
)
×
(
)
–
130
–
=
2941
0.018 A
------------------------------------
2
55
28
+
(
)
×
(
)
–
110
–
=
V
T/R
4 V
+
Z
T/R
2R
P
--------------------------
Vamp =
v
T/R
1
Z
T/R
-----------
+
Λ
Λ
–
V
T/R
[Z
T/R
]
V
AMP
–
+
R
P
R
P
+