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參數(shù)資料
| 型號(hào)： | HC5515CP |
| 廠商： | INTERSIL CORP |
| 元件分類： | 模擬傳輸電路 |
| 英文描述： | ITU CO/PABX SLIC with Low Power Standby |
| 中文描述： | TELECOM-SLIC, PDIP22 |
| 封裝： | PLASTIC, DIP-22 |
| 文件頁數(shù)： | 11/17頁 |
| 文件大?。?/td> | 170K |
| 代理商： | HC5515CP |
65
Cases 2 and 3 illustrate the longitudinal loop current. The
definition of a longitudinal loop current is a common mode
current, that flows either out of or into tip and ring
simultaneously. Longitudinal currents in the on-hook state
result in
equal
currents flowing through the sense resistors
R
1
and R
2
(Figure 17). And longitudinal currents in the off-
hook state result in
unequal
currents flowing through the
sense resistors R
1
and R
2
. Notice that for case 2,
longitudinal currents flowing away from the SLIC, the current
through R
1
is the metallic loop current plus the longitudinal
current; whereas the current through R
2
is the metallic loop
current minus the longitudinal current. Longitudinal currents
are generated when the phone line is influenced by
magnetic fields (e.g. power lines).
Loop Current Detector
Figure 17 shows a simplified schematic of the loop current
detector. The loop current detector works by sensing the
metallic current flowing through resistors R
1
and R
2
. This
results in a current (I
RD
) out of the transconductance
amplifier (gm
1
) that is equal to the product of gm
1
and the
metallic loop current. I
RD
then flows out the R
D
pin and
through resistor R
D
to V
EE
. The value of I
RD
is equal to:
The I
RD
current results in a voltage drop across R
D
that is
compared to an internal 1.25V reference voltage. When the
voltage drop across R
D
exceeds 1.25V, and the logic is
configured for loop current detection, the DET pin goes low.
The hysteresis resistor R
H
adds an additional voltage
effectively across R
D
, causing the on-hook to off-hook
threshold to be slightly higher than the off-hook to on-hook
threshold.
Taking into account the hysteresis voltage, the typical value
of R
D
for the on-hook to off-hook condition is:
ON
HOOK to OFF
–
HOOK
–
Taking into account the hysteresis voltage, the typical value
of R
D
for the off-hook to on-hook condition is:
OFF
HOOK to ON
–
HOOK
–
A filter capacitor (C
D
) in parallel with R
D
will improve the
accuracy of the trip point in a noisy environment. The value
of this capacitor is calculated using the following Equation:
D
where: T = 0.5ms.
Ring Trip Detector
Ring trip detection is accomplished with the internal ring trip
comparator and the external circuitry shown in Figure 18.
The process of ring trip is initiated when the logic input pins
are in the following states: E0 = 0, C1 = 1 and C2 = 0. This
logic condition connects the ring trip comparator to the DET
output, and causes the Ringrly pin to energize the ring relay.
The ring relay connects the tip and ring of the phone to the
external circuitry in Figure 18. When the phone is on-hook
the DT pin is more positive than the DR pin and the DET
output is high. For off-hook conditions DR is more positive
than DT and DET goes low. When DET goes low, indicating
that the phone has gone off-hook, the SLIC is commanded
by the logic inputs to go into the active state. In the active
state, tip and ring are once again connected to the phone
and normal operation ensues.
Figure 18 illustrates battery backed unbalanced ring injected
ringing. For tip injected ringing just reverse the leads to the
phone. The ringing source could also be balanced.
NOTE: The DET output will toggle at 20Hz because the DT input is
not completely filtered by C
RT
. Software can examine the duty cycle
and determine if the DET pin is low for more that half the time, if so
the off-hook condition is indicated.
I
RD
I
-----------------------------------
I
–
I
---------
=
=
(EQ. 24)
R
D
--------------------------------------------------------------------------
=
(EQ. 25)
R
D
--------------------------------------------------------------------------
=
(EQ. 26)
C
D
-------
=
(EQ. 27)
HC5515
DET
R
D
R
2
gm
1
gm
1
(I
METALLIC
)
R
D
C
D
V
REF
1.25V
+
-
CURRENT
LOOP
COMPARATOR
V
EE
-5V
I
RD
R
H
RING
TIP
+
-
R
1
+
-
CASE 1
CASE 2
CASE 3
I
METAL-
LIC
I
LONGITUDI-
NAL
I
LONGITUDI-
NAL
DIGITAL MULTIPLEXER
+
-
FIGURE 17. LOOP CURRENT DETECTOR
HC5515
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