參數(shù)資料
型號(hào): L9219A
英文描述: CAP CER 390PF 3.15KVDC R3 RAD
中文描述: 低成本線接口,具有反向電池和雙電流限制
文件頁數(shù): 19/30頁
文件大?。?/td> 397K
代理商: L9219A
Agere Systems Inc.
19
Data Sheet
November 2001
with Reverse Battery and Dual Current Limit
L9219A/G Low-Cost Line Interface
Applications
(continued)
dc Applications
Battery Feed
The dc feed characteristic can be described by:
where:
I
L
= dc loop current.
V
T/R
= dc loop voltage.
|
V
BAT
|
= battery voltage magnitude.
V
OH
= overhead voltage. This is the difference between
the battery voltage and the open loop tip/ring
voltage.
R
L
= loop resistance, not including protection resistors.
R
P
= protection resistor value.
R
dc
= SLIC internal dc feed resistance.
Notes:
V
BAT
= –48 V.
I
LIM
= 22 mA.
R
dc1
= 80
.
Figure 13. Loop Current vs. Loop Voltage
Starting from the on-hook condition and going through
to a short circuit, the curve passes through the follow-
ing two regions:
Region 1: On-hook and low loop currents. The slope
corresponds to the dc resistance of the
SLIC, R
dc1
(default is 70
typical). The open
circuit voltage is the battery voltage minus
the overhead voltage of the device, V
OH
(default is 6.5 V typical). These values are
suitable for most applications, but can be
adjusted if needed. For more information,
see the sections entitled Adjusting dc Feed
Resistance and Adjusting Overhead Voltage.
Region 2: Current limit. The dc current is limited to a
starting value determined by external resis-
tor R
PROG
, the logic table, an internal current
source, and the gain from tip/ring to pin
VITR.
Current Limit
With the logic inputs set to 11 (a low current limit active
state), current limit with a 100
load is given by the fol-
lowing:
0.637 R
PROG
(k
) + 2 mA = I
LIM
x (mA)
Via the logic table, the current limit can be increased a
nominal 42% from the value set by the R
PROG
resistor.
The relationship between low current limit and high
current limit is as follows:
= 0.7
Overhead Voltage
In order to drive an on-hook ac signal, the SLIC must
set up the tip and ring voltage to a value less than the
battery voltage. The amount that the open loop voltage
is decreased relative to the battery is referred to as the
overhead voltage and is expressed as the following
equation:
V
OH
= |V
BAT
| – (V
PT
– V
PR
)
Without this buffer voltage, amplifier saturation will
occur and the signal will be clipped. The L9219 is auto-
matically set at the factory to allow undistorted on-hook
transmission of a 3.14 dBm signal into a 900
loop
impedance.
V
T/R
R
L
2R
P
---------------------------------------------
R
dc
L
+
+
=
I
L
R
L
+
R
dc
+
2R
P
---------------------------------
=
0
10
20
50
0
20
30
40
50
LOOP VOLTAGE (V)
30
40
10
L
1
12.5 k
–1
R
dc1
I
LIM
TESTED
I
LIM
ONSET
12-3050 (F).i
LIMIT
Low
I
LIMIT
High
(
(
)
)
-I
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