IA3223-C-FU Silicon Laboratories Inc, IA3223-C-FU Datasheet - Page 32

• Manufacturer Part Number: IA3223-C-FU
• Description: IC EZ DAA SYST SIDE WORLD 16QSOP
• Manufacturer: Silicon Laboratories Inc
• Series: EZ DAA™r

Specifications of IA3223-C-FU

• Function: Data Access Arrangement (DAA)
• Interface: Serial
• Number Of Circuits: 1
• Voltage - Supply: 3 V ~ 3.6 V
• Current - Supply: 7.9mA
• Power (watts): 2W
• Operating Temperature: -25°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Includes: "911" Detection, Line-In-Use Detection, Parallel Pick-Up Detection, Ring Detection
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

Line in Use and Line Disconnect
The LIU detector is a DC line-voltage threshold detector. One of four levels (~2.5, 15, 22.5, and 30V) can be selected. Unfortunately,
line-in-use status is ambiguous for voltages between 12V and 19V. Central Office lines and short-range digital loop carrier systems
always provide at least 21V of on-hook voltage. Some PBXs and VoIP boxes may supply less. Telephone devices will generally work
with less than 12V at a loop current of 20-30mA. Users sometimes add in-line Zener devices (available at Radio Shack
with answering machines in order to improve parallel-pickup disconnect performance. These in-line Zener devices increase the
answering machine’s off hook voltage by 6 to 8V, often pushing the total off-hook voltage above 15V. On short loops with 60mA
capability, some telephone devices may drop over 12V when off hook. European telephone devices with CTR-21 current limiting may
even exceed 32V when off hook on short lines, especially in France.
For most situations, the 15V LIU threshold setting should be the default. A simple technique to reduce ambiguity is to use both LIU
and snoop audio detection. A more sophisticated method is to have the system learn normal on and off hook voltages by stepping
through the LIU levels of 15, 22.5 and 30V while using the snoop circuit to monitor audio.
The 2.5V threshold setting is intended to differentiate a disconnected line (not plugged in) from a powered line without attempting to
distinguish on hook from off hook. A disconnected line may create erratic 2.5V and line-reversal detection. This is because the Line
Side has over 5 MΩ input resistance. Less than 100 nA of on-hook loop current can trigger the 2.5V threshold. This behavior is
similar to putting a standard 10 MΩ input voltmeter on a long open line and seeing several Volts due to static or leakage. Generally,
a valid line is present only if the voltage is stable above 3V and not reversing. If it is below 2V or reversing, the line should be
considered disconnected. Off-hook loop-current reversal (if available on a trunk) occurs only after dialing to indicate far party answer
(toll call).
The LineStat Pin as Interrupt (On Hook)
The LineStat pin is an active-low interrupt output. Because it has an open-drain output with a weak internal pull-up resistor, it can be
wire-ORed with other interrupts in the system. When LineStat is active, the system must determine the cause of the interrupt based
on history and the state of the DAA. The table below suggests criteria for qualifying the interrupt when the DAA is on hook:
Audio Snooping
The snoop circuit does not have the same audio performance as the off-hook receiver path, but it is adequate for Caller ID decoding
and line monitoring. Snoop audio recovers from all high voltage line signals in less than 10 ms and is continuously present. Besides
Caller ID, snooping can be used to monitor the line for call logging or used for voice/fax steering. If a fax calling tone or a specific
DTMF sequence is detected, the DAA may be instructed to seize the line. Since DTMF signals normally have higher amplitude than
Caller ID signals, a -6 dB gain setting exists for the snoop path (SGAIN set to zero), which allows monitoring of up to 4 VPP signals
without clipping.
Theory of Operation— Off-Hook Line Status
In the off-hook state, the same gyrator circuit that is used for on-hook line-status monitoring is reconfigured to filter audio signals
from the line-current change circuit (parallel-pickup detector), so that changes in loop current can be measured without spurious
parallel-pickup signals from normal audio. Capacitor CExt2 with an internal 1.2 MΩ resistor forms large time constant that stores the
average DC value of the received signal. This DC value is compared with short-term changes to detect loop current drops caused by a
parallel phone on the line going off hook. Sensitivity to parallel pickup is also affected by the IA3222 Line-Side’s holding and AC-input
capacitor values. There are four levels of parallel-pickup sensitivity, programmed by register bits LTH0 and LTH1. Each setting is
about twice as sensitive as the previous. When a parallel-pickup event occurs it causes a temporary active state both at the PPU
(Parallel Pick Up) bit and at the LineStat pin.
LSR required setting
High
Low
Possible Cause of Interrupt
Ringing
Line reversal
Line in use
Line no longer in use
Line activity
Criterion
Expected ring cadence both at LineStat pin and at RNG bit
LP bit changed compared to before interrupt, stable for 100 ms
LIU bit high if previously low, stable for 100 ms
LIU bit low if previously high, stable for 100 ms
No ring cadence or change in LP or LIU bits
IA3222/IA3223
®
) in series
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