IA3223-C-FU Silicon Laboratories Inc, IA3223-C-FU Datasheet - Page 38

• 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

IA3222/IA3223
excessive voltages and power. From the telephone system side, a line cross might occur if a power line falls across the telephone
line shorting to one side of the line. Power-line cross is different than lightning surges because of its longer duration. This makes it
much more dangerous even though it is less likely than lightning surges. Failure can occur either from isolation breakdown or from
consequent excessive voltage between Tip and Ring, which can create a fire hazard in the DAA.
A power-line cross may start out as a longitudinal high-voltage event but may quickly turn into a metallic event. When a power line
gets connected to one side or the other of the telephone line, it may cause the primary surge suppressor to trigger, which in turn
burns open, leaving the AC mains on one side of the phone line. Then, either if the telephone device goes off hook, or if the
breakover diode triggers, the other primary arrestor may trigger, creating a path directly through the DAA for the AC power line. In this
scenario, there may be very little telephone line resistance in the current loop (less than 50 m of line) to limit the current. The result
is a destructive failure of the DAA. It may burst into flames due to continuous pouring of energy into the DAA surge suppressor, which
is normally not capable of continuous currents above 1A.
Safe differential line-crossing failure, when required, only means that the product needs to fail safely on a line cross, i.e. not burst
into flames during the test. Designing a DAA to survive a line cross is possible but at a significant cost. The simple method is to use
an expensive 600 V
PTC (Positive Temperature Coefficient) resetable fuse.
AC
If the DAA needs to provide safe differential line-crossing failure, the normal solution is to have some type of slow fusible link. Fast-
blow fuses will likely get blown by lightning transients and are therefore not recommended. There also exist special (and costly)
telecom fuses that will survive a 25A peak Type B surge but will blow on a differential line cross event. Another solution is to use a 5
to 10 Ω, 1 to 2 W, flame-proof metal-oxide resistor for a fusible link. With some testing and care, this cheaper solution will withstand
the Type B surge but safely blow on a line-crossing event. (Contact Silicon Labs for possible resistor types.) This also has the
advantage of limiting the surge current that results from asymmetrical firing of the primary lightning arrestors. Any fusible link needs
to be flame proof and physically separate from the PC board, since the UL 1459 test ramps the AC voltage slowly up to 600 V
to
AC
allow components to generate heat and possibly start a fire, rather than just blow apart. If a component such as a metal oxide
resistor begins to glow and is lying flat on the PC board, it will carbonize the PC board material, which may lead to conductive
tracking (carbonized insulator becoming conductive) and possibly fire.
Common-Mode Noise from the Mains Supply
A hidden common-mode noise issue arises from the absence of the third (green) wire safety ground in home AC power wiring. In the
US, third-wire grounds and three-prong AC outlets were not installed extensively until the mid-1950’s and were not required by code
until the early 1960’s. Europe and other countries have similar histories. Thus in older homes third-wire grounds are missing in some
or all rooms, even if three-prong sockets are present. When computer equipment with switching supplies is plugged into such an
outlet, up to half of the AC mains voltage can be measured on the chassis ground relative to real earth ground (or the telephone)
line. The reason is that most computer switching supplies have pi network power-line EMI filters that have RF decoupling capacitors
in the nF range tied between live, neutral and ground. If the third-wire ground is not actually grounded, the capacitors in the filter
create a divider between live and neutral with the third-wire ground. It is possible to get a slight electrical shock from a computer
chassis just from this effect. More significantly, it creates a very large common-mode noise voltage between the phone line (in effect
a ground connection) and the local, ungrounded ground wiring.
This large AC common-mode voltage sometimes causes overload problems on resistor-capacitor isolated Caller ID circuits. The
IAI3222 does not have this issue since it is completely isolated. Even with otherwise isolated DAAs, EMI immunity capacitors, if
mismatched, can introduce noise on the telephone line, especially if large AC line transients are present. For example, if two 470 pF
EMI capacitors are mismatched by 5%, the 23.5 pF unbalance has an impedance of 2.3 MΩ at 3 kHz. Against a typical line
impedance of 600 Ω, this represents 72 dB of common-mode balance. If the power line has 20 V audio-band transients and the third
wire ground is disconnected, this results in 10V at the chassis and will inject about 2.6 mV of audio noise on the phone line, enough
to disrupt most high-speed (V.90, V.34, V.32) modem communication. For this reason, EMI bypass capacitors, when they are
necessary, should be of the lowest value necessary to reduce EMI to the desired level.
Worse yet, some capacitively-coupled DAAs use more than 60 pF of signal-isolation capacitance that is not balanced relative to Tip
and Ring. Even without EMI capacitors, significant noise can be injected into the line if the system third-wire ground is floating.
Similarly, base-band linear opto-isolated DAAs can inject line noise even though the capacitive coupling across the isolation barrier
may be less than 1 pF. The reason is that opto-isolated systems need a gain of almost 100 on the transfer and servo photodiodes
because of the typical 1 % current-transfer ratio. Normally, there is a small amount of isolation capacitance in the sensitive servo or
transfer photodiode to the effect that at 3 kHz the common-mode balance may be 80dB or less.
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