HC55120CM INTERSIL [Intersil Corporation], HC55120CM Datasheet - Page 17

• Manufacturer Part Number: HC55120CM
• Description: Low Power Universal SLIC Family
• Manufacturer: INTERSIL [Intersil Corporation]

(AC) 2-Wire to 4-Wire Gain
The 2-wire to 4-wire gain is equal to V
From Equation 18 with V
Substituting Equation 24 into Equation 23 and simplifying.
By design, VTX = -VTX´, therefore
A more useful form of the equation is rewritten in terms of
V
from E
Rearranging Equation 27 in terms of E
into Equation 26 results in an equation for 2-wire to 4-wire
gain that’s a function of the synthesized input impedance of
the SLIC (Z
HC55120, HC55121, HC55130, HC55131, HC55140, HC55141, HC55142, HC55143, HC55150, HC55151
Loop Equation
–
V
G
V
E
G
E
TX
G
TX
TR
2-4
2-4
G
=
/V
+
=
=
=
=
Z
I
TR
G
V
---------- =
V
---------- - =
V
M
L
E
----------------------- - E
Z
–
TX
I
TX
TR
TR
+
G
to V
I
-
M
E
I
. A voltage divider equation is written to convert
M
Z
-
Z
M
G
TR
L
+
TR
+
Z
+
2R
Z
TR
I
--------------------------------------- -
Z
Z
-----------------------------
TR
L
M
Z
I
) and the protection resistors (R
L
TR
M
TR
P
Z
as shown in Equation 27.
Z
–
I
Z
M
TR
TR
Z
- 2R
2R
G
L
V
TR
–
TR
+
–
RING
P
V
TIP
Z
2R
TX
P
TR
+
-
RX
P
+
-
=
4-17
=
= 0
R
R
I
I
0
M
M
P
P
-------------------------------- -
Z
V
+
Z
-
TR
TX
L
´
+
+
-
–
Z
2R
TR
TX
G
FIGURE 17. SIMPLIFIED AC TRANSMISSION CIRCUIT
P
, and substituting
/E
R
S
20
R
20
G
S
with V
P
+
-
R
500K
R
).
500K
20
I
INT
INT
X
I
X
20
RX
+
-
(EQ. 27)
(EQ. 23)
(EQ. 24)
(EQ. 25)
(EQ. 26)
(EQ. 28)
UniSLIC14
= 0
+
+
-
-
1/80K
I
Z
T
= 200 (Z
Notice that the phase of the 2-wire to 4-wire signal is in
phase with the input signal.
(AC) 4-Wire to 4-Wire Gain
The 4-wire to 4-wire gain is equal to V
From Equation 18.
Substituting -V
Equation 30.
Substituting Equation 21 for V
simplifying results in Equation 31.
(AC) 2-Wire Impedance
The AC 2-wire impedance (Z
into the SLIC, including the fuse resistors. The formula to
calculate the proper Z
shown in Equation 32.
Equation 32 can now be used to match the SLIC’s
impedance to any known line impedance (Z
V
V
G
Z
TX
TX
T
4 4
TR
–
=
I
X
=
- 2R
5
=
200
=
– V
–
2
P
I
-----------
V
V
V
X
)
TX
RX
TX
RX
Z
TR
500K
500K
=
–
=
TR
V
-------------------------------------------- -
– V
–
–
2
TR
2
/Z
2R
V
Z
----------------------- -
Z
RX
A
L
Z
L
P
L
= I
TR
into Equation 29 for I
T
+ 2R
Z
+
I
+
X
500K
L
M
for matching the 2-wire impedance is
2
Z
–
(Z
I
TR
M
500K
2R
+
TR
P
-
A = 1
Z
-2R
P
TR
TR
TR
P
) is the impedance looking
–
)
in Equation 30 and
2R
P
V
V
PTG
TX
TX
RX
/V
M
RX
TR
results in
, E
).
V
G
V
TX
RX
+
= 0.
-
+
-
(EQ. 32)
(EQ. 29)
(EQ. 30)
(EQ. 31)