參數(shù)資料
型號(hào)： HC5513BIM
廠商： INTERSIL CORP
元件分類(lèi)： 模擬傳輸電路
英文描述： TVS UNI-DIR 40V 1500W SMC
中文描述： TELECOM-SLIC, PQCC28
封裝： PLASTIC, LCC-28
文件頁(yè)數(shù)： 8/18頁(yè)
文件大?。?/td> 175K
代理商： HC5513BIM
61
Circuit Operation and Design Information
The HC5513 is a current feed voltage sense
S
ubscriber
L
ine
I
nterface
C
ircuit (SLIC). This means that for short loop
applications the SLIC provides a programed constant current to
the tip and ring terminals while sensing the tip to ring voltage.
The following discussion separates the SLIC’s operation into
its DC and AC path, then follows up with additional circuit
and design information.
Constant Loop Current (DC) Path
SLIC in the Active Mode
The DC path establishes a constant loop current that flows
out of tip and into the ring terminal. The loop current is
programmed by resistors R
DC1
, R
DC2
and the voltage on
the R
DC
pin (Figure 13). The R
DC
voltage is determined by
the voltage across R
1
in the saturation guard circuit. Under
constant current feed conditions, the voltage drop across R
1
sets the R
DC
voltage to -2.5V. This occurs when current
flows through R
1
into the current source I
2
. The R
DC
voltage
establishes a current (I
RSN
) that is equal to V
RDC
/(R
DC1
+R
DC2
). This current is then multiplied by 1000, in the loop
current circuit, to become the tip and ring loop currents.
For the purpose of the following discussion, the saturation
guard voltage is defined as the maximum tip to ring voltage
at which the SLIC can provide a constant current for a given
battery and overhead voltage.
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.
NOTE: 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.
HC5513
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
HC5513
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