L3234 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
L3234 Datasheet PDF : 26 Pages
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L3234 - L3235
Table 1.
OPERATING
MODE
ACTIVE
RINGING
STAND-BY
INPUT PIN
LINE STATUS
OUTPUT PIN
SBY
RNG
0: ON HOOK
1: OFF HOOK
0: NO GND KEY
1: GND KEY ON
OH
GDK
PU
CS
0
0
0
0
0
0
0
0
1
0
0
1
0
1
1
1
0
1
0
0
0
0
0
0
1
0
0
1
0
0
0
0
0
1
0
0
1
0
0
1
1
0
1
1
0
1
1
0
1
1
0
0
0
0(*)
0
0
1
0
0(*)
1
0
0
0
0(*)
1
0
X
1
1
X
X
1
1
1
0
X
1
1
0
1
(*)This status is latched and doesn’t change until RNG turn to 0
OPERATING MODES
Stand-By (SBY = 1 and RNG = 0)
In Stand-By mode the L3235 limits the DC Loop
current to 3 mA.
In this mode all the AC circuits are active and all
the AC characteristics are the same as in Active
Mode.
Also the two Line Current detectors (hook and
GND key) are active but due to the loop current
limited to 3 mA they will not be activated.
This mode is useful in emergency condition when
it is very important to limits the system power dis-
sipation.
Ringing Mode (SBY = 0 and RNG = 1)
When ringing mode is selected "CS" pin is set to
1 in order to activate the L3234 ringing injector.
See L3234 for detailed description.
Ring trip is detected by means of the same inter-
nal circuitry used for off-hook detection.
An off-hook delay time lower than 1⁄2 FRING should
be selected. (see ext. components list).
When ring trip is detected "CS" is automatically
set to "0" allowing in this way a quick ringing dis-
connection.
After Ring trip detection the Card Controller must
set the L3235 in active mode to remove the inter-
nal latching of the "CS" information.
Active mode (SBY = 0 and CS1 = 0)
In Active mode the L3235 has the DC charac-
teristic show in Fig.13
The DC characteristics of L3235 has two different
feeding conditions:
1)Current Limiting Region : (short loop) the DC
impedance of the SLIC is very high (>20
Kohm) therefore the system works as a cur-
rent generator. By the ext. resistor RLIM con-
nected at pin 19 it is possible to program limit-
ing current values from 20 mA to 70 mA.
2) Voltage source region (long loop).
The DC impedance of the L3235 is almost
equal to zero therefore the system works like
a voltage generator with in series the two ex-
ternal protection resistors Rp.
When a limiting current value higher than 40 mA
is programmed the device will automatically re-
duce to 40 mA the loop current for very short
loop.
This is done in order to limit the maximum power
dissipation in very short loop to values lower than
2W for the external transistor and lower than
0.5W for the L3235 itself.
This improve the system reliability reducing the
L3235 power dissipation and therefore the inter-
nal junction temperature.
14/26
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