參數(shù)資料
型號(hào)： HC5526
廠商： Intersil Corporation
英文描述： ITU CO/PABX SLIC with Low Power Standby(用戶線接口電路（SLIC))
中文描述： 國(guó)際電聯(lián)合作/交換機(jī)用戶接口的低功耗待機(jī)（用戶線接口電路電路（SLIC））
文件頁(yè)數(shù)： 8/19頁(yè)
文件大?。?/td> 234K
代理商： HC5526
8
For loop resistances that result in a tip to ring voltage less than
the saturation guard voltage the loop current is defined as:
where: I
L
= Constant loop current.
R
DC1
and R
DC2
= Loop current programming resistors.
Capacitor C
DC
between R
DC1
and R
DC2
removes the VF
signals from the battery feed control loop. The value of C
DC
is determined by Equation 2:
where T = 30ms.
The minimum C
DC
value is obtained if R
DC1
= R
DC2
.
Figure 14 illustrates the relationship between the tip to ring
voltage and the loop resistance. For a 0
loop resistance both
tip and ring are at V
BAT
/2. As the loop resistance increases, so
does the voltage differential between tip and ring. When this
differential voltage becomes equal to the saturation guard
voltage, the operation of the SLIC’s loop feed changes from a
constant current feed to a resistive feed. The loop current in the
resistive feed region is no longer constant but varies as a
function of the loop resistance.
Figure 15 shows the relationship between the saturation guard
voltage, the loop current and the loop resistance. Notice from
Figure 15 that for a loop resistance <1.2k
(R
SG
= 21.4k
) the
SLIC is operating in the constant current feed region and for
resistances >1.2k
the SLIC is operating in the resistive feed
region. Operation in the resistive feed region allows long loop
and off-hook transmission by keeping the tip and ring voltages
off the rails. Operation in this region is transparent to the
customer.
The Saturation Guard circuit (Figure 13) monitors the tip to
ring voltage via the transconductance amplifier A
1
. A
1
generates a current that is proportional to the tip to ring
voltage difference. I
1
is internally set to sink all of A
1
’s
current until the tip to ring voltage exceeds 12.5V. When the
tip to ring voltage exceeds 12.5V (with no R
SG
resistor) A
1
supplies more current than I
1
can sink. When this happens
A
2
amplifies its input current by a factor of 12 and the current
through R
1
becomes the difference between I
2
and the
output current from A
2
. As the current from A
2
increases, the
voltage across R
1
decreases and the output voltage on R
DC
decreases. This results in a corresponding decrease in the
loop current. The R
SG
pin provides the ability to increase the
saturation guard reference voltage beyond 12.5V. Equation 3
HC5526
V
TX
R
RX
R
DC1
R
DC2
C
DC
RSN
R
DC
I
RSN
TIP
RING
-2.5V
I
RING
I
TIP
A
2
I
TIP
I
RING
R
SG
R
SG
-5V
LOOP CURRENT
CIRCUIT
SATURATION GUARD
CIRCUIT
A
1
I
1
I
2
R
1
+
-
+
-
+
-
+
-
-5V
FIGURE 13. DC LOOP CURRENT
-5V
I
L
DC1
R
DC2
----------------+
1000
×
=
(EQ. 1)
C
DC
T
DC1
---------------
DC2
---------------
+
×
=
(EQ. 2)
0
1.2K
-50
-40
-30
-20
-10
0
V
BAT
= -48V, I
L
= 23mA, R
SG
= 21.4k
SATURATION
GUARD VOLTAGE
LOOP RESISTANCE (
)
V
TIP
V
RING
RESISTIVE FEED
REGION
T
CONSTANT CURRENT
FEED REGION
SATURATION
GUARD VOLTAGE
∞
FIGURE 14. V
TR
vs R
L
0
10
20
30
0
10
20
30
40
50
LOOP CURRENT (mA)
T
V
BAT
= -24V, R
SG
=
∞
V
BAT
= -48V, R
SG
= 21.4k
SATURATION GUARD
VOLTAGE, V
TR
= 38V
RESISTIVE FEED
REGION
CONSTANT CURRENT
FEED REGION
R
RSG
= 21.4k
R
RSG
=
∞
100k
100k
4k
1.5k
2k
700
<400
<1.2k
R
L
R
L
SATURATION GUARD
VOLTAGE, V
TR
= 13V
FIGURE 15. V
TR
vs I
L
and R
L
HC5526
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