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參數資料
| 型號： | HC-5502X |
| 廠商： | Intersil Corporation |
| 英文描述： | () |
| 中文描述： | （） |
| 文件頁數： | 2/17頁 |
| 文件大小： | 255K |
| 代理商： | HC-5502X |
4-2
The SLIC must be able to sense this DC current and flag the
switch controller: This is referred to as Switch Hook
Detection (SHD). It tells the switch controller that the line is
busy, and is a supervisory function.
The subscriber set is often located very close to the switch
office. Thus, the loop resistance will be very low and the SLIC
should incorporate a feedback network that will limit the loop
current to a specified maximum to prevent battery power drain
and minimize power dissipation at the board level. The HC-
5502X/4X SLICs sense the loop current and adjust the
voltage on the ring side of the line to cause line current
saturation.
The telephone can be rung by switching a ring relay to
connect a ring generator to the loop. The on-off switching of
the relay (cadencing) is controlled by the Ring Command
(RC) input which gates the relay driver output. When the
user answers the telephone, the ring relay is automatically
tripped, the ring command signal is inhibited and the 2W
loop is made ready for voice transmission. Voice signals are
transmitted onto the loop by directly modulating the DC feed.
This AC voice signal is coupled to the users earpiece via a
transformer in the telephone set. Voice transmission for the
2W to the 4W system is called the hybrid function. For 2W to
4W transmission, the subscriber talking into his set
modulates the resistance of the telephone microphone. This
causes AC current in the loop which is sensed by the SLIC
and transmitted as a ground referenced voltage signal to the
signal processing electronics within the switch.
Subscriber loops are usually measured in terms of loop
resistance. The nominal loop length is 1200
. Owing to the
length of the lines and their location near power lines,
common mode or longitudinal currents are often induced.
The SLIC has to distinguish between these noise signals
(longitudinal) and the transversal signals, and reject the
unwanted longitudinal components: this is a measure of the
SLIC's longitudinal balance. The primary noise sources are
60/50Hz power lines, cable cross talk, and R
F
transmissions.
The Intersil SLICs will accommodate 15mA
RMS
of noise
currents on each side of the loop.
The line is also subjected to lightning strikes. Together with
primary and secondary protection networks, the SLIC must
withstand 1kV peak of lightning induced energy. In fact, the
plastic encapsulated Intersil SLIC can withstand a 1kV peak
strike with a small signal diode bridge providing voltage
clamping and current steering.
The Intersil HC-5502X/4X
The HC-5502X/4X family of SLICs are primary intended for
use within Private Branch Exchanges (PBX) although they
can be used in the larger switch networks found in Central
Offices (CO).
Figure 2 shows the functional schematic of the SLIC. The
subfunctions to be described are:
Line Feed Amplifiers
Transversal Amplifiers
Loop Current Limiting: Metallic, Fault and Thermal
Limiting
Ring Trip and Ground Key Detection
Spare or Uncommitted Operational Amplifier
Logic Network
Line Feed Amplifiers
The line feed amplifiers are high power op amps, and are
connected to the subscriber loop through 300
of feed
resistance; the configuration is shown in Figure 3. The feed
resistors provide a 600
balanced load for the 2W to 4W
transmission, and limit longitudinal currents; the two
resistors immediately adjacent to the feed amplifiers function
as sense resistors for 2W to 4W transmission and signalling
purposes.
The tip feed amplifier is configured as a unity gain non-
inverting buffer. A -4V bias (derived from the negative battery
(V
B-
) in the bias network) is applied to the input of the
amplifier. Hence, the tip feed DC level is at -4V. The principal
reason for this offset is to accommodate sourcing and
sinking of longitudinal noise currents up to 15mA
RMS
without saturating the amplifier output. The tip feed amplifier
also feeds the ring feed amplifier, which is configured as a
unity gain inverting amplifier as seen from the TF amplifier.
The noninverting input to the R
F
amp is biased at a VB-/2.
Looking into this terminal the amplifier has a noninverting
gain of 2. Thus, the DC output at ring feed is:
V
RF
(DC) = (4 + V
B-
) Volts
For a -48V battery, V
RF
= -44V. Hence, the nominal battery
feed across the loop provided by the SLIC is 40V. When the
subscriber goes off-hook this DC feed causes current
(metallic current) to flow around the loop.
The received audio signal V
RX
from the switch is fed into the
tip feed amplifier and appears at the TF terminal. It is also
fed through the ring feed amplifier and is inverted. Thus, a
differential signal of 2V
RX
appears across the line: for a
600
line this compensates the 6dB loss due to the 600
of
line feed resistance. The V
RX
signal causes AC audio
currents to flow around the loop which are then AC coupled
to the earpiece of the telephone set. Figure 4 shows the
single ended AC equivalent circuit of the subscriber loop for
voice transmission. In the general case the signal design
equation for 4W to 2W transmission is given by:
V
LINE
Z
Z
LINE
----------+
2V
RX
×
=
Application Note 549
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相關代理商/技術參數 |
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| HC5503 | 制造商:INTERSIL 制造商全稱:Intersil Corporation 功能描述:Low Cost 24V SLIC For PABX / Key Systems |
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| HC5503CB | 制造商:Rochester Electronics LLC 功能描述: 制造商:Intersil Corporation 功能描述: |
| HC5503CB96 | 制造商:Rochester Electronics LLC 功能描述:HC5503CB (TAPE&REEL) - Bulk |
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