le79r70 Zarlink Semiconductor, le79r70 Datasheet - Page 12

• Manufacturer Part Number: le79r70
• Description: Ringing Subscriber Line Interface Circuit
• Manufacturer: Zarlink Semiconductor

Loop-Threshold Detect Equations
Z
Z
R
R
C
C
R
R
R
R
T
RX
DC1
DCR1
DC
DCR
D
LTH
LTH
LTH
=
=
=
=
+
500 Z
R
=
=
=
=
R
+
----------- -
G
19 ms
LTH
Z
------------ -
12.67
------------ -
11.37
----------------------------- R
R
---------------------------------------- • 150 µs
DC2
42L
R
V
(
R
R
L
R
DCR1
DCR2
BAT1
D
D
DCR1
2WIN
•
915
•
=
12.67
•
------------------------------------------------- -
Z
for high battery
for low battery
-------------- -
I
R
---------------------------------
T
+
2500
LOOP
=
–
R
R
–
DC1
+
10
R
DCR2
DC1
--------------------- -
Iringlim
2R
1000 Z
500 Z
for high battery state
DCR2
3000
•
+
F
R
)
(
R
DC2
D
•
DC2
L
–
+
400
T
2R
–
F
)
2R
F
Table 2. User-Programmable Components
Zarlink Semiconductor Inc.
Z
R
puting Z
pacitance between VTX and RSN must be taken into account.
Z
desired receive gain.
R
I
R
See Applications Circuit for these components.
C
150 µs.
R
loop-resistance threshold between on-hook and off-hook detection. R
should be greater than 56 kΩ to guarantee detection will occur in the
Standby state. Choose the value of R
the equation for R
This is the same equation as for R
solved for R
For low battery, the detect threshold is slightly higher, which will avoid
oscillating between states.
R
antee no unstable states under all operating conditions. This equation
will show at what resistance the standby threshold will be; it is actually
a current threshold rather than a resistance threshold, which is shown
by the Vbat dependency.
LOOP
T
RX
F
DC1
DCR1
DCR
D
LTH
, and Z
is connected between the VTX and RSN pins. The fuse resistors are
is the resistor connected from the RD pin to GND and R
is connected from V
, R
standby < R
12
sets the ringing time constant, which can be between 15 µs and
is the desired loop current in the constant-current region.
, R
DC2
T
, the internal current amplifier pole and any external stray ca-
DCR2
2WIN
, and C
LTH
, and C
is the desired 2-wire AC input impedance. When com-
.
LTH
LTH
DC
DCR
active V
to find where the threshold is for low battery.
form the network connected to the RDC pin.
RX
form the network connected to the RDCR pin.
to R
BAT1
SN
. Z
< R
D
T
in the preceding equation, except
D
is defined above, and G
LTH
for high battery state; then use
active V
BAT2
, which will guar-
LTH
42L
is the
is the
D