ATTL7554BP Agere Systems, ATTL7554BP Datasheet - Page 23

• Manufacturer Part Number: ATTL7554BP
• Description: L7554 Low-Power SLIC
• Manufacturer: Agere Systems

Data Sheet
March 1997
Applications
dc Applications
Ring Trip Detection
The ring trip circuit is a comparator that has a special in-
put section optimized for this application. The equiva-
lent circuit is shown in Figure 31, along with its use in an
application using unbalanced, battery-backed ringing.
Figure 31. Ring Trip Equivalent Circuit and
The comparator input voltage compliance is V
V
direction. Its application is straightforward. A resistance
(R
current that is repeated in the R
lower resistance (R
input. When ringing is being injected, no dc current
flows through R
potential than R
flows, the R
parator. In Figure 31, a low-pass filter with a double
pole at 2 Hz was implemented to prevent false ring trip.
The following example illustrates how the detection cir-
cuit of Figure 31 will trip at 12.5 mA dc loop current us-
ing a –48 V battery.
Lucent Technologies Inc.
BAT
HOOK SWITCH
TSN
RC PHONE
PHONE
, and the maximum current is 240 A in either
+ R
402
R
R
TS2
LOOP
TS1
Equivalent Application
TSP
) in series with the R
V
V
BAT
274 k
R
RING
input voltage increases to trip the com-
TS1
TSN
TS2
(continued)
, so the R
TSP
. When enough dc loop current
I
N
C
0.27 µF
(continued)
RTS2
) is placed in series with the R
=
=
2 M
2 M
R
R
TSN
TSP
17.9 A
–7 – (–48)
-------------------------- -
2.289 k
TSP
C
0.022 µF
RTS1
R
R
TSP
TSN
TSP
input is at a lower
TSN
+
–
I
input. A slightly
P
15 k
input establishes a
= I
I
N
N
+
–
7 V
CC
to
12-3014 (C)
NRDET
TSP
The current I
ator input. The voltage at comparator input R
Using this equation and the values in the example, the
voltage at input R
(I
below R
through R
will trip. In this example,
Ring Ground Detection
Pin ICM sinks a current proportional to the longitudinal
loop current. It is also connected to an internal compar-
ator whose output is pin RGDET. In a ground start
application where Tip is open, the ring ground current
is half differential and half common mode. In this case,
to set the ring ground current threshold, connect a
resistor R
according to the following relation:
The above equation is shown graphically in Figure 18.
It applies for the case of Tip open. The more general
equation can be used in ground key application to
detect a common-mode current I
LOOP(dc)
V
R T S P
TSN
= 0). Input R
ICM
TS1
. When enough dc loop current flows
=
N
from pin ICM to V
to raise its dc drop to 5 V, the comparator
is repeated as I
V
R
R
BAT
I C M
TSP
I C M
I
LOOP dc
+
is –12 V during ringing injection
k
TSP
k
I
=
L O O P dc
L7554 Low-Power SLIC
is, therefore, at a level of 5 V
12.5 mA
=
=
=
V
--------------------- -
I
V
-------------------
I
P
---------------- -
402
CC
RG
CM
CC
CC
in the positive compar-
5 V
CM
. Select the resistor
R
mA
mA
:
120
T S 1
60
+
I
P
TSP
R
T S P
is:
23