ia3211 integration, ia3211 Datasheet - Page 6

• Manufacturer Part Number: ia3211
• Description: Optical Silicon Daa Modem/lineside Chipset
• Manufacturer: integration

Hence, the resulting frequency of the RNG signal is either the
exact incoming ring frequency (similar to a standard
optocoupler based ring detection circuit design) or 2 times that
value which may require some adjustments in the host
firmware.
Line reversal detection
On-hook Line Reversal Detection
On-hook line reversal detection is specifically useful for Caller
ID operations in certain countries such as United Kingdom for
instance. Upon detection of a line reversal occurrence,
provided the proper minimum level requirements are met, the
IA3211 and IA3212 chipset generates a single 4ms wide pulse
on the RING output signaling the system’s application that such
an event as occurred. It is up to the system’s application to
discriminate between an incoming ring, which would generate a
series of pulses, and a line reversal single pulse.
On-hook line reversal detection is only possible when the
device is configured in full wave ring detection scheme (HLFWV
unconnected).
Off-hook Line Reversal Detection
Off-hook line reversal detection is mostly used in PABX
application where its occurrence triggers the billing mechanism
at the central office level. The IA3123 chipset outputs a single
4ms wide positive pulse on its LSTAT output upon detection of
such an event. This mechanism is the same as the line voltage
drop detection described in the LIU/PPU detection chapter; it is
up to the system’s application to discriminate between those
two type of events.
Layout Considerations
The two most important aspects to consider when designing a
DAA are noise and isolation. Electrical isolation is the easier
topic to understand and
specifications require very high voltage isolation between the
loop circuit and the user circuit as a safety issue. The IA3211
and IA3212 chipset design uses opto-isolators to achieve an
Ring Signal
Full Wave
Half Wave
detector
detector
deal with. Most telephone
isolation barrier of up to 2500 volts. This isolation can only be
realized if the circuit board design and construction is also
capable of withstanding this kind of high voltage. The line side
circuit should be physically separated from the user (modem)
side circuit with at least a 0.2-inch (5 mm) wide gap. The two
opto-isolators must be the only components to straddle the
gap. Ideally, the line connection (usually an RJ-11 jack) is
mounted on the edge of the PC board and surrounded by the
line side components, including the IA3212. The amount of
circuitry will depend on the specific application, and which
country requirements are being designed. All other circuitry,
including the IA3211, must be located on the other side of the
gap.
It is important that no conductive material be inside, or under
the barrier. If the PCB is a multi layer design, insure that ground
or voltage planes do not pass under the barrier. Noise is the
other major layout related issue. A compact layout is also very
good at keeping induced noise to a minimum. Being an analog
circuit, the IA3211 and IA3212 chipset will not generate
significant noise by itself. However, the circuit can (and will)
pick up noise generated from nearby digital circuits. Keeping
the line side circuits inside a small, tightly designed isolation
barrier as shown will minimize noise pickup. Using a separate
ground plane for the line side components is usually not
needed. In fact, ground planes can be highly detrimental if
ground loops develop. If there is to be a ground plane, then
connect it only to the IA3212 VSS on the line side pin.
A common problem with noise pickup is when the IA3211 is
interfaced to a modem data pump IC (or other applications) Be
sure that the ACREF, pin 18, is well by-passed with at least a
100nF high frequency capacitor. Similar bypassing of the VDD
pin is also good engineering practice. In some applications,
digital noise can be injected into the IA3211 via the control
pins (such as OFFHK or SNP). If this happens, try adding a 3.3k
resistor in series with the line and a small bypass capacitor and
the IA3211 input pin.
Another potential problem is the need to reject local RF pickup
from the telephone line itself. The local loop, being a very long
pair of wires, is an excellent receiving antenna. Local broadcast
and TV signals will inevitably find their way into the DAA from
the Loop. Prudent designers will add the necessary
components to reject such interfering signals. Techniques for
RFI reduction include adding a ferrite bead to the loop wires
directly adjacent to the RJ11 connector, and adding ferrite
beads to the DAA circuit itself, in conjunction with high voltage
by-pass
specifications require such RFI filtering.
capacitors.
Some
international
IA3211 & IA3212
telephone
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