參數(shù)資料
型號(hào)： HC55140IMZ
廠商： INTERSIL CORP
元件分類： 模擬傳輸電路
英文描述： Low Power Universal SLIC Family
中文描述： TELECOM-SLIC, PQCC28
封裝： ROHS COMPLIANT, PLASTIC, MS-018AB, LCC-28
文件頁(yè)數(shù)： 17/36頁(yè)
文件大?。?/td> 701K
代理商： HC55140IMZ
17
FN4659.13
June 1, 2006
example R
D
is calculated to be 41.6k
(500/12mA). The
next closest standard value is 41.2k
.
R
D
= I
SHD
The true value of ISH-, for the selected value of R
D
is given
by Equation 8:
For the example above, ISH- equals 7.28mA (500 x 0.6/
41.2K). Verify that the value of ISH- is above the suspected
line leakage of the application. The UniSLIC family will
provide a constant on hook voltage level for leakage currents
up to this value of line leakage.
The R
OH
resistor, which
is used to set the offhook
overhead voltage, is
calculated using
Equations 9 and 10.
I
OH
is defined as the
difference between the
I
LOOP(min)
and ISH-.
Substituting Equation 8
for ISH- into Equation 9 and solving for R
OH
defines R
OH
in
terms of I
LOOP(min)
and R
D
.
OH
Equation 10 can be used to determine the actual ISH- value
resulting from the R
D
resistor selected. The value of R
D
should be the next standard value that is lower than that
calculated. This will insure meeting the I
LOOP(min)
requirement. ROH for the above example equals 39.1k
.
The current limit is set by a single resistor and is calculated
using Equation 11.
LOOP(max)
The maximum loop
resistance is calculated
using Equation 12. The
resistance of the
protection resistors
(2R
P
) is subtracted out
to obtain the maximum
loop length to meet the
required off hook
overhead voltage. If R
LOOP(MAX)
meets the loop length
requirements you are done. If the loop length needs to be
longer, then consider adjusting one of the following: 1) the
SHD threshold, 2) minimum loop current requirement or 3)
the on and off hook signal levels.
V
I
LOOP(min)
SLIC in the Active Mode
Figure 17 shows a simplified AC transmission model. Circuit
analysis yields the following design equations:
Substitute Equation 14 into Equation 15
Substitute Equation 16 into Equation 17
Substitute Equation 18 into Equation 19
Substituting -V
TR
/Z
L
into Equation 20 for I
M
and rearranging
to solve for V
TR
results in Equation 21
where:
V
RX
= The input voltage at the VRX pin.
V
A
= An internal node voltage that is a function of the loop
current detector and the impedance matching networks.
I
X
= Internal current in the SLIC that is the difference
between the input receive current and the feedback current.
I
M
= The AC metallic current.
R
P
= A protection resistor (typical 30
).
Z
T
= An external resistor/network for matching the line
impedance.
V
TX
′
= The tip to ring voltage at the output pins of the SLIC.
------------
(EQ. 7)
ISH- = R
D
---------
(0.6)
(EQ. 8)
V
BH
V
SAT
V
OH(off)
2.5V
OFF HOOK
OVER HEAD
T
LOOP CURRENT
I
LOOP(min)
DC FEED CURVE
ISH-
I
OH
R
OH
---------
LOOP(min)
-------------------------------------------
=
=
(EQ. 9)
R
OH
=
R
500
D
LOOP(min)
-----------------------------------------------------------
(EQ. 10)
R
LIM
=
-----------------------------
(EQ. 11)
V
BH
V
SAT
V
OH(off)
2.5V
T
LOOP CURRENT
I
LOOP(min)
DC FEED CURVE
R
LOOP(MAX)
R
LOOP(max)
=
(
)
+
]
------------–
-2R
P
(EQ. 12)
V
A
= I
M
2R
S
---------
200
×
Z
TR
2R
P
–
(
)
×
5
×
×
(EQ. 13)
V
A
I
M
2
-------
Z
TR
2R
P
–
(
)
=
(EQ. 14)
V
------------
-
V
------------
= I
X
Node Equation
(EQ. 15)
I
X
V
------------
-
I
Z
-----------------------------------------
2R
–
(
)
=
(EQ. 16)
I
X
500k - V
TX
′
+ I
X
500k = 0
Loop Equation
(EQ. 17)
V
TX
′
2V
RX
I
M
Z
TR
2R
P
–
(
)
–
=
(EQ. 18)
V
TR
-I
M
2R
P
+ V
TX
′
= 0
Loop Equation
(EQ. 19)
V
TR
I
M
Z
TR
2V
RX
–
=
(EQ. 20)
V
TR
1
Z
L
----------
+
2
–
V
RX
=
(EQ. 21)
HC55120, HC55121, HC55130, HC55140, HC55142, HC55143, HC55150
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