參數(shù)資料
型號： L8567-44PLCC
英文描述： Telecommunication IC
中文描述： 通信集成電路
文件頁數(shù)： 33/42頁
文件大?。?/td> 701K
代理商： L8567-44PLCC
Lucent Technologies Inc.
33
Data Sheet
August 1999
People’s Republic of China Applications
L8567 SLIC for
dc Characteristics
The L8567 SLIC operates in a dc unbalanced mode. In
the forward active state, under open-circuit (on-hook)
conditions, the tip to ring voltage will be a nominal
7.1 V less than the battery. This is the overhead volt-
age. The tip and ring overhead is achieved by biasing
ring a nominal 4.6 V above battery and by biasing tip a
nominal 2.5 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 below.
12-3431 (F)
Figure 26. Tip/Ring Voltage Decrease
As illustrated above, as loop length decreases, the tip
to ground voltage will decrease with a slope corre-
sponding to one-half the internal dc feed resistance of
the SLIC. (The L8567 dc feed resistance is a nominal
110
.) 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 of the SLIC
plus approximately 10 k
, which is the slope of the I/V
characteristic in the current-limit region.
The dc feed characteristic can be described by:
V
T/R
=
Where:
I
L
= dc loop current.
V
T/R
= dc loop voltage.
|V
BAT
| = battery voltage magnitude.
V
OH
= overhead voltage. This is the difference between
the battery voltage and the open loop tip/ring
voltage.
R
L
= loop resistance, not including protection resistors.
R
P
= protection resistor value.
R
dc
= SLIC internal dc feed resistance.
The design begins by drawing the desired dc template.
Refer to Figures 23, 24, and 26.
Starting from the on-hook condition and going through
to a short circuit, the curve passes through two regions:
Region 1; On-hook and low loop currents: The slope
corresponds to the dc resistance of the SLIC, R
dc1
(plus
any series resistance). The open-circuit voltage is the
battery voltage less the overhead voltage of the device,
V
OH
(7.0 V typical).
Region 2; Current limit: The dc current is limited to a val-
ue determined by external resistor R
PROG
. This region of
the dc template has a high resistance (10 k
).
Calculate the external resistor as follows:
R
PROG
(k
) = 1.59 I
LIM
(mA)
Notice that the I/V curve is uninterrupted when the
power is shifted from the high-voltage battery to the
low-voltage battery (if auxiliary battery option is used),
if the transition occurs in the current-limit region of
operation. This is shown in Figure 24.
VTIP TO GND
ON HOOK
(1/2)R
dc
BEGIN CURRENT LIMITING
(1/2)R
dc
(1/2)R
dc
+ R
LIM
DECREASING LOOP LENGTH
V
BAT
I
L
R
L
+
R
dc
+
2R
P
---------------------------------
=
R
L
--------------------------------------------
R
dc
L
2R
P
+
+
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