PBL38772/1 데이터 시트보기 (PDF) - Ericsson
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PBL38772/1 Datasheet PDF : 24 Pages
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PBL 387 72
Loop Monitoring Functions
The loop current, ground key and ring-trip detectors report
their status through a common output, DET. The particular
detector to be connected to the detector pin, DET, is selected
via the three bit control interface C1, C2 and C3. Please
refer to section Control Inputs for a description of the control
interface.
Detector Output (DET)
The PBL 387 72/1 SLIC incorporates a detector output driver
designed as an open collector (npn), an internal 10 kΩ pull-up
resistor to VCC. The emitter of the drive transistor is con-
nected to AGND. The logic high,1, level is 5 V and the logic
low,0, is AGND.
Loop Current Detector
The loop current detector indicates that the telephone is off-
hook and that dc current is flowing in the loop by setting
the output pin DET to a logic low level when selected. The
loop current detector threshold value, ILTh, where the loop
current detector changes state, is programmable with the RLD
resistor. RLD connects between pin PLD and ground and is
calculated according to:
RLD
=
500
ILTh
The loop current detector is internally filtered and is not
influenced by the ac signal at the two-wire side. In the Tip
Open Circuit state the DET output changes to logic low state
when the RINGX current exceeds ILTh.
Ground Key Detector, Loop Ground Fault Detector
The ground key detector circuit senses the difference
between TIPX and RINGX currents. When triggerd the output
pin DET is set to a logic high level. The detector is triggered
when the difference exceeds the internally set and fixed
current threshold. Diagnostics: loop ground faults can be
detected by the ground key detector.
Loop voltage measurement
The loop voltage, VTR (V), is presented at the DET output
as a pulse train with a repetition frequency, fV (Hz), which is
inversely proportional to the voltage according to:
fV
=
106
(|VTR| +
1)
The loop voltage measurement commences when
commanding the SLIC into the loop voltage measurement
state from any other state (refer to Table 1, SLIC operating
states). Loop diagnostic purposes and setting line card gain
are two examples of uses for the loop voltage information.
Control Inputs
The PBL 387 72/1 SLIC has three digital control inputs, C1,
C2 and C3. A decoder in the SLIC interprets the control input
condition and determing the commanded operating state. C1,
C2 and C3 are internal pull-up inputs. The logic inputs are
compatible with a 3.3V logic interface.
Open circuit state (C3, C2, C1 = 0,0,0)
In the Open Circuit State the TIPX and RINGX line drive
amplifiers as well as other circuit blocks are powered down.
This causes the SLIC to present a high impedance to the
line. Power dissipation is at a minimum and no detectors are
active. DET output is set high.
Ringing state (C3, C2, C1 = 0,0,1)
The low voltage ringing signal, which is connected to VR,
is amplified and appears at TIPX and RINGX as a balanced
high voltage ring signal. The ring-trip detector monitors hook
status and sets the DET output low when off-hook line status
is detected.
Active state (C3, C2, C1 = 0,1,0)
TIPX is the terminal closest to ground and sources loop
current while RINGX is the more negative terminal and sinks
loop current. The loop current detector is activated. The loop
current detector indicates off-hook with a logic low level
present at the detector output.
Active state, loop voltage measurement
(C3, C2, C1 = 0,1,1)
A frequency inversely proportional to the line voltage will
appear at the DET output when the PBL 387 72/1 is set to the
active, loop voltage measurement state.
Active state, ground key and Loop Ground Fault
Detector (C3, C2, C1 = 1,0,1)
TIPX is the terminal closest to ground and sources loop
current while RINGX is the more negative terminal and sinks
loop current. The ground key detector is activated. The
ground key detector will indicate active ground key with a
logic high level present at the detector output. This state is
also used for a diagnostic function as loop ground faults can
be detected by the ground key detector
Active polarity reversal state, loop current detector (C3,
C2, C1 = 1,1,0)
TIPX and RINGX polarity is reversed compared to the Active
State: RINGX is the terminal closest to ground and sources
loop current while TIPX is the more negative terminal and
sinks current. The loop current detector is activated. The loop
current detector will indicate off-hook with a logic low level
present at the detector output.
20
EN/LZT 146 136 R1A © Ericsson Microelectronics, December 2001
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