ia3222 integration, ia3222 Datasheet - Page 30

• Manufacturer Part Number: ia3222
• Description: Ia3222/ia3223 Ez Daa? Chipset With Analog Interface
• Manufacturer: integration

IA3222/IA3223
LINE MONITORING
Theory of Operation—On-Hook Line Status
The IA3222/3223 chipset was designed to provide maximum information about the telephone line—both AC and DC—to allow
intelligent line management, and to allow automatic telephone devices to share the line with human-controlled applications
gracefully. Automatic DAA applications may be found in set-top boxes, alarm systems, fax machines, meter readers, remote-
diagnostic modems, answering machines, VoIP boxes, etc. A key feature of the IA3223 is the LineStat pin, which can be programmed
to generate an interrupt if the line status changes either while in the on-hook state or in the off-hook state. This reduces the need for
continuous polling of the line-status bits.
In the on-hook state, the IA3222 Line Side chip converts the line voltage to a frequency at the rate of 2 kHz per Volt. The V-to-f’s
operating range is from ±3V to over ±150V. This frequency is sent as pulses across the capacitor isolation barrier. The pulse duty
cycle contains line-polarity information. The V-to-f converter’s frequency is sufficient to allow the IA3223 System Side to decode all
DC line voltage, ring signals, line reversals and audio information (Caller ID, DTMF, and other tone monitoring). While monitoring the
line in the on-hook state, the Line Side loads the line with no less than 5 MΩ DC resistance. This allows continuous monitoring while
exceeding regulatory minimum idle-line resistance requirements.
The IA3223 System Side chip receives the frequency-encoded voltage information and converts it back to continuous representation
of the line voltage. The voltage difference between the ACRef pin and the CExt2 pin is about 1/200th of the line voltage. Since the
DC source resistance of CExt2 is about 75 kΩ, any measurement system resistance should exceed 10 MΩ to prevent excessive
loading.
For the on-hook snoop function, CExt1 is part of a gyrator circuit that separates the large DC line voltage from the low-level AC
voltage, so that the line audio signal may be amplified without excessive offset. CExt1 sets the low-frequency corner on this gyrator
circuit inversely proportional to its value. With 10 nF, the -3 dB corner is around 240 Hz and the slope is 6 dB per octave. The upper-
frequency corner is around 4 kHz. It is set by internal RC values, and is therefore not adjustable by the user. The upper-frequency
roll-off exceeds 18 dB per octave.
In the on-hook state, CExt2 filters the line voltage analog with a time constant of CExt2 times 75 kΩ, for separating the AC ring signal
from the DC line voltage. With a CExt2 of 220 nF, the corner frequency is about 10 Hz. The ring-detection circuit compares the
voltage on CExt2 with an internal unfiltered signal. If it exceeds one of the four programmable thresholds in one direction, a ring-
detection condition occurs. This produces a standard half-wave ring-detection signal that works similarly to a standard opto-isolator
ring-detection circuit.
In addition to ring detection, the other on-hook functions are a line-polarity (LP) detector, a line-in-use detector (LIU) and a line-
activity (LACT) detector. The LIU detector measures if the line voltage exceeds one of four programmed voltage levels. The LACT
detector output is activated if the line voltage changes by more than 10 to 20V, thus acting like a sensitive full-wave ring detector. All
of these signals can be read from IA3223 registers. Depending on the setting of the LSR bit, either the ring-detection signal or the
LACT signal can be output to the LineStat (line status) pin.
Ringing
The IAI 3223 supports conventional ring-detection algorithms that produce an on-off digital output when the AC signal exceeds a
preset threshold. The period between cycles is measured by the system firmware to within 1-2ms to allow qualification of ring cycles
in order to differentiate them from other line signals: notably on-/off-hook transients, dial pulses and test signals sent by the
telephone company. The ring-detection state is presented on read-only register RNG bit and may optionally be multiplexed to the
LineStat pin. The width of the ring-detection pulse is always at least 20 % of the ring period for sine-wave ring signals.
Many regulatory ring requirements have disappeared in the last fifteen years and the usage of pulse dialing has also decreased. In
more ancient telephone history, when telephone companies were monopolies, 10 V
signals were sent down telephone lines in
RMS
order to determine how many ringer loads were present. Although this probably no longer occurs, conventional wisdom is that ring
detectors should not trip below 10 V
. Many country-specific regulations and EIA/TIA recommendations support this requirement
RMS
to this day.
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