HC5515 Intersil Corporation, HC5515 Datasheet - Page 10

• Manufacturer Part Number: HC5515
• Description: ITU CO/PABX SLIC with Low Power Standby
• Manufacturer: Intersil Corporation

For applications where the 2-wire impedance (Z
Equation 15) is chosen to equal the line impedance (Z
expression for A
(AC) 4-Wire to 4-Wire Gain
The 4-wire to 4-wire gain is equal to V
From Equations 9, 10 and 11 with E
Transhybrid Circuit
The purpose of the transhybrid circuit is to remove the
receive signal (V
preventing an echo on the transmit side. This is
accomplished by using an external op amp (usually part of
the CODEC) and by the inversion of the signal from the
4-wire receive port (RSN) to the 4-wire transmit port (V
Figure 16 shows the transhybrid circuit. The input signal will
be subtracted from the output signal if I
analysis yields the following equation:
The value of Z
Where V
Therefore:
---------- -
R
Z
A
A
V
Z
B
4 2
4 4
TX
TX
B
–
–
=
=
+
–
R
V
V
-----------
=
=
R
Z
TR
TX
RX
B
TX
–
V
-----------
V
RX
---------- -
Z
RX
TX
Z
+
-
RX
=
/V
T
Z
---------- -
Z
V
-----------
V
RX
0
TX
=
T
B
RX
Z
TX
L
1
-- -
2
–
4-2
is then:
RX
---------- -
Z
equals 1/ A
+
-
Z
------------ -
1000
------------------------------------------- -
E
RX
Z
G
T
) from the transmit signal (V
Z
simplifies to:
T
TR
Z
RING
L
------------------------------------------- -
------------ -
1000
+
TIP
Z
+
2R
T
2R
Z
F
L
+
4-4
F
64
+
+
2R
R
R
I
I
Z
M
M
2R
F
F
.
L
F
F
+
V
TX
Z
G
+
-
L
TX
= 0:
1
FIGURE 15. SIMPLIFIED AC TRANSMISSION CIRCUIT
/V
equals I
HC5515
RX
.
TX
TR
2
), thereby
. Node
,
(EQ. 19)
(EQ. 20)
(EQ. 21)
(EQ. 22)
(EQ. 23)
+
-
L
), the
TX
1
).
HC5515
A = 250
A = 250
Example:
Given: R
value), R
The value of Z
Supervisory Functions
The loop current and the ring trip detector outputs are
multiplexed to a single logic output pin called DET. See Table
1 to determine the active detector for a given logic input. For
further discussion of the logic circuitry see section titled
“Digital Logic Inputs”.
Before proceeding with an explanation of the loop current
detector and the longitudinal impedance, it is important to
understand the difference between a “metallic” and
“longitudinal” loop currents. Figure 17 illustrates 3 different
types of loop current encountered.
Case 1 illustrates the metallic loop current. The definition of
a metallic loop current is when equal currents flow out of tip
and into ring. Loop current is a metallic current.
HC5515
F
TX
= 20 and Z = 600 ,
= 20k , Z
FIGURE 16. TRANSHYBRID CIRCUIT
V
RSN
B
TX
= 18.7k
A = 4
Z
T
RX
R
TX
= 280k , Z
Z
RX
V
RSN
I
TX
1000
I
2
1
I
M
Z
B
T
Z
T
= 562k (standard
R
Z
FB
RX
V
V
CODEC/
FILTER
TX
-
+
RX
+
-
+
-
V
RX
+
-
V
TX
+
-