Lucent Technologies Inc.
35
Data Sheet
August 1999
People’s Republic of China Applications
L8567 SLIC for
dc Applications
(continued)
On-Hook Transmission
(continued)
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:
where V
SAT
is the combined internal saturation voltage
between the tip/ring amplifiers and V
BAT
(4.0 V typical).
R
P
(
) is the protection resistor value. Z
T/R
(
) is the ac
loop impedance.
Example:
Determine the required overhead to transmit on-hook
(I
LOOP
= 0) a 3.17 dBm ac signal into a 900
ac lead.
Assume use of 50
protection resistors with a 10%
tolerance or 55
and an L7583 solid-state switch. The
worst-case resistance of the switch is 28
. Note the
minimum overhead voltage of the L8567 is 6.4 V.
55
28
+
[
×
900
V
ON
= 4.0 +
3.17 dBm = 20log
Vrms = 1.296 V
V
ON
= 4.0 +
Vrms = 1.296 V
V
ON
= 4.0 +
V
OH
= 6.17 V < 6.4 V
Thus, an overhead of 6.17 V is needed for on-hook
transmission of a 3.17 dBm signal into a 900
ac load.
The L8567 has a minimum overhead of 6.4 V.
Supervision
Both the loop closure and ring trip supervision func-
tions are included on the L8567 SLIC. The outputs of
these two supervision functions are internally wired-
ORed together to form a single output NSTAT. The
wired-OR connection of the loop supervision and ring
trip detector is also available on pin NLED. This pin has
sufficient drive capability to drive an LED. This pin is an
open-collector output, so multiple pins can be used to
drive a common LED. Also included is a SLIC thermal
shutdown indicator, NTSD.
Note that the ring trip detector is not active in the low-
power scan state. The ring trip detector must be active
prior to applying power ringing to the subscriber loop.
Activate the ring trip detector by putting the L8567 SLIC
into the powerup mode before applying power ringing
to the subscriber loop.
Loop Closure
The on-hook to off-hook loop closure threshold is inter-
nally set to a nominal 11 mA at V
BAT
= –48 V. There is a
nominal 2 mA hysteresis. This means that the off-hook
to on-hook threshold will be a nominal 2 mA less than
the on-hook to off-hook threshold. The loop closure
threshold will track with battery voltage, increasing as
the battery gets more negative. The loop closure com-
parator has built-in longitudinal rejection, eliminating
the need for an external 50 Hz/60 Hz filter. The loop
closure detector is valid during scan, forward, and
reverse active states.
V
OH
V
SAT
1
Z
T/R
-----------
+
v
T/R
+
=
Λ
1
]
2
+
2 V
rms
)
900
10
------rms
-----------------------------
]
2
1
2
55
900
28
+
[
]
×
+
2 V
rms
)
1
2 55
28
+
]
900
+
2
(
)
1.296
(
)