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參數(shù)資料
| 型號： | HC5526IP |
| 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)： | 12/18頁 |
| 文件大?。?/td> | 176K |
| 代理商： | HC5526IP |
68
Figure 19 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.
Longitudinal Impedance
The feedback loop described in Figure 20(A, B) realizes the
desired longitudinal impedances from tip to ground and from
ring to ground. Nominal longitudinal impedance is resistive
and in the order of 22
.
In the presence of longitudinal currents this circuit
attenuates the voltages that would otherwise appear at the
tip and ring terminals, to levels well within the common mode
range of the SLIC. In fact, longitudinal currents may exceed
the programmed DC loop current without disturbing the
SLIC’s VF transmission capabilities.
The function of this circuit is to maintain the tip and ring
voltages symmetrically around V
BAT
/2, in the presence of
longitudinal currents. The differential transconductance
amplifiers G
T
and G
R
accomplish this by sourcing or sinking
the required current to maintain V
C
at V
BAT
/2.
When a longitudinal current is injected onto the tip and ring
inputs, the voltage at V
C
moves from it’s equilibrium value
V
BAT
/2. When V
C
changes by the amount
V
C
, this change
appears between the input terminals of the differential
transconductance amplifiers G
T
and G
R
. The output of G
T
and G
R
are the differential currents
I
1
and
I
2
, which in
turn feed the differential inputs of current sources I
T
and I
R
respectively. I
T
and I
R
have current gains of 250 single
ended and 500 differentially, thus leading to a change in I
T
and I
R
that is equal to 500(
I
) and 500(
I
2
).
The circuit shown in Figure 20(B) illustrates the tip side of
the longitudinal network. The advantages of a differential
input current source are: improved noise since the noise due
to current source 2I
O
is now correlated, power savings due
to differential current gain and minimized offset error at the
Operational Amplifier inputs via the two 5k
resistors.
Digital Logic Inputs
Table 1 is the logic truth table for the TTL compatible logic
input pins. The HC5526 has two enable inputs pins (E0, E1)
and two control inputs pins (C1, C2).
The enable pin E0 is used to enable or disable the DET
output pin. The DET pin is enabled if E0 is at a logic level 0
and disabled if E0 is at a logic level 1.
The enable pin E1 gates the ground key detector to the DET
output with a logic level 0, and gates the loop or ring trip
detector to the DET output with a logic level 1.
A combination of the control pins C1 and C2 is used to
select 1 of the 4 possible operating states. A description of
each operating state and the control logic follow:
Open Circuit State (C1 = 0, C2 = 0)
In this state the SLIC is effectively off. All detectors and both
the tip and ring line drive amplifiers are powered down,
presenting a high impedance to the line. Power dissipation is
at a minimum.
HC5526
DET
R
D
R
2
gm
1
gm
2
gm
1
(I
METALLIC
)
R
D
C
D
V
REF
1.25V
+
-
CURRENT
LOOP
COMPARATOR
V
EE
-5V
GROUND
KEY
COMPARATOR
gm
2
(I
TIP
- I
RING
)
I
RD
R
H
I
1
D
1
D
2
I
GK
RING
TIP
+
-
R
1
+
-
CASE 1
CASE 2
CASE 3
I
METALLIC
←
I
LONGITUDINAL
I
LONGITUDINAL
→
DIGITAL MULTIPLEXER
+
-
+
-
R
H
FIGURE 18. LOOP CURRENT AND GROUND KEY DETECTORS
TIP
RING
HC5526
R
RT
V
BAT
E
RG
R
3
R
4
R
2
R
1
DR
DT
RING TRIP
COMPARATOR
DET
C
RT
RINGRLY
RING
RELAY
+
-
FIGURE 19. RING TRIP CIRCUIT FOR BATTERY BACKED RINGING
HC5526
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