3222/3223-DB1 Silicon Laboratories Inc, 3222/3223-DB1 Datasheet - Page 31

• Manufacturer Part Number: 3222/3223-DB1
• Description: EVAL BOARD FOR IA3222/3223
• Manufacturer: Silicon Laboratories Inc
• Series: EZ DAA™r

Specifications of 3222/3223-DB1

• Main Purpose: Telecom, Data Acquisition Arrangement (DAA)
• Embedded: Yes, FPGA / CPLD
• Utilized Ic / Part: IA3222, IA3223
• Primary Attributes: -
• Secondary Attributes: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

6.5. 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 30 V) can be
selected. Unfortunately, line-in-use status is ambiguous for voltages between 12 V and 19 V. Central Office lines
and short-range digital loop carrier systems always provide at least 21 V of on-hook voltage. Some PBXs and VoIP
boxes may supply less. Telephone devices will generally work with less than 12 V at a loop current of 20–30 mA.
Users sometimes add in-line Zener devices (available at Radio Shack®) in series 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 8 V, often pushing the total off-hook voltage above 15 V. On short loops with
60 mA capability, some telephone devices may drop over 12 V when off hook. European telephone devices with
TBR-21 current limiting may even exceed 32 V when off hook on short lines.
For most situations, the 15 V 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 30 V while using the snoop circuit to
monitor audio.
The 2.5 V 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 2.5 V and line-
reversal detection. Generally, a valid line is present only if the voltage is stable above 3 V and not reversing. If it is
below 2 V 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).
6.6. 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. Table 11 suggests criteria for
qualifying the interrupt when the DAA is on-hook.
6.7. 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.
LSR Required
Setting
High
Low
Line no longer in use
Possible Cause of
Table 11. Interrupt Qualifying Criteria (On-Hook)
Line reversal
Line activity
Line in use
Interrupt
Ringing
Rev. 5.0
LP bit changed compared to before interrupt, stable for 100
Expected ring cadence both at LineStat pin and at RNG bit
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
Criterion
ms
IA3222/23
31