參數(shù)資料
型號： L7557
廠商： Lineage Power
英文描述： Low-Power SLICs （electronic subscriber loop interface circuits ）with Battery Switch(帶電池開關(guān)的低功耗用戶環(huán)路線接口電路（SLIC）)
中文描述： 低功耗SLIC組件（電子用戶環(huán)路接口電路）與電池開關(guān)（帶電池開關(guān)的低功耗用戶環(huán)路線接口電路電路（SLIC））
文件頁數(shù)： 23/28頁
文件大小： 753K
代理商： L7557
Lucent Technologies Inc.
23
Data Sheet
January 2000
with Battery Switch
L7556, L7557 Low-Power SLICs
Applications
(continued)
dc Applications
(continued)
Ring Trip Detection
The ring trip circuit is a comparator that has a special
input 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 ring-
ing.
12-3014.f (F)
Figure 31. Ring Trip Equivalent Circuit and
Equivalent Application
The comparator input voltage compliance is V
CC
to
V
BAT
, and the maximum current is 240 μA in either
direction. Its application is straightforward. A resistance
(R
TSN
+ R
TS2
) in series with the R
TSN
input establishes a
current which is repeated in the R
TSP
input. A slightly
lower resistance (R
TSP
) is placed in series with the R
TSP
input. When ringing is being injected, no dc current
flows through R
TS1
, and so the R
TSP
input is at a lower
potential than R
TSN
. When enough dc loop current
flows, the R
TSP
input voltage increases to trip the com-
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
using a –48 V battery.
I
N
=
= 17.9 μA
The current I
N
is repeated as I
P
in the positive compar-
ator input. The voltage at comparator input R
TSP
is:
V
RTSP
V
BAT
I
LOOP dc
+
=
Using this equation and the values in the example, the
voltage at input R
TSP
is –12 V during ringing injection
(I
LOOP(dc)
= 0). Input R
TSP
is therefore at a level of 5 V
below R
TSN
. When enough dc loop current flows
through R
TS1
to raise its dc drop to 5 V, the comparator
will trip. In this example,
I
LOOP(dc)
=
= 12.5 mA
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 resis-
tor R
ICM
from pin ICM to V
CC
. Select the resistor
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
CM
:
+
–
R
LOOP
15 k
7 V
I
P
= I
N
RTSN
RTS2
2 M
2 M
C
RTS2
0.27
μ
F
C
RTS1
0.022
μ
F
274 k
PHONE
HOOK SWITCH
RC PHONE
V
RING
V
BAT
NRDET
R
TS1
402
R
TSP
I
N
RTSN
–
+
R
TSP
2.289 k
)
-----------------------------
)
R
TS1
I
P
R
TSP
×
+
×
402
------------------
R
ICM
k
(
)
(
)
----------------------
=
R
ICM
k
(
)
I
CM
mA
(
)
---------------------
=
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