TC04A-200.TD Ver la hoja de datos (PDF) - Semtech Corporation
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TC04A-200.TD Datasheet PDF : 8 Pages
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TC04A-200
PROTECTION PRODUCTS
Applications Information
SLIC protection Concepts
Transient immunity standards require telecommunica-
tions equipment be surged in all of its operating states.
This refers to the on-hook state (ring generator or
ring detection monitoring) and the off-hook state
(operational state). The On-Hook state must allow for
operation of the normal battery voltage and ring
voltage without interference. The Off-Hook state only
allows for operation of the battery voltage plus opera-
tion signals.
SLIC Operating Voltages (Unbalanced Ringing)
Several SLIC types exist. The first type of SLIC requires
an external ring relay to disconnect the SLIC and
connect the ringing and trip bias power supply generat-
ing the ringing signal. Protection must be provided for
the subsystem which includes the ringing relay and
ringing source. This type of ringing is sometimes called
unbalanced ringing. The ringing voltage is typically
inserted on the Ring (B-lead), while the Tip (A-lead) is
grounded. The SLIC may or may not be protected by
the ringing subsystem protection. Separate subsystem
protection may be needed and must have a minimum
operating voltage that exceeds the battery voltage and
the ring signal voltage. The SLIC IC is disconnected
Balanced Ringing
from the line and the ring generator and does not see
0V
Tip
the ringing voltages. Therefore, the protection element
for the SLIC must only have a minimum operating
voltage greater than the battery supply voltage. This
device must suppress all transients above ground and
below the battery voltage.
The second SLIC type has an integrated ring generation
capability. The protection device described in this
application information is particularly suited for use
with this SLIC type. Unlike the unbalanced system
described above, these SLIC devices generate a
balanced ring signal between Tip & Ring. The voltage on
either line falls between the battery voltage and
ground. Therefore, the SLIC protection device can have
an operating voltage that is very close to the battery
voltage. Since battery voltages may vary between talk
and ringing states, it is desirable to utilize a program-
mable protection device so that the voltage across the
SLIC does not exceed the process limits and the stress
on the device is minimized.
Battery
Ring
Protecting SLIC with Integrated Ring Generator
ã 2000 Semtech Corp.
4
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