IA3223-C-FU Silicon Laboratories Inc, IA3223-C-FU Datasheet - Page 37

• 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
Metallic (differential) surges arise from the longitudinal lightning surges causing either the asymmetric triggering of the primary
arrestors, or arcing of only one side of the line to ground (if only one primary arrestor is functioning). To protect against metallic
surges, a DAA uses a surge suppressor that clamps the differential voltage to prevent damage. Good solutions provide surge
immunity for both on-hook and off-hook DAA states. Protecting the off-hook state requires some form of current limiting to protect
the off-hook path during the surge. Breakover diodes generally work better since they collapse the surge voltage, thus reducing the
energy dissipated in the off-hook circuit over 100 times. MOVs can be used for surges, but because of their nearly two-to-one spread
between minimum and maximum clamp voltages, the hook switch must be capable of withstanding much higher peak voltages than
with breakover diodes. In addition, the hook circuit must turn itself off (blanking) during the surge in order to prevent excess
dissipation.
Because the primary arrestors are not typically in a mutually triggered pair (unlike some gas tubes) during a common mode high
voltage transient, one arrestor will always fire before the other. Ironically, on a telephone product with a breakover secondary surge
protection diode between tip & ring, this can lead to overstress of this diode especially if the primary arrestors have a breakover
characteristic (carbon gap, gas tube, or semiconductor breakover diode). The reason is that once a primary arrestor triggers on one
side of the line, the longitudinal surge becomes metallic. This triggers the secondary breakover diode in the telephone product. At
that point the other primary arrestor won’t trigger at all, since there is now a low-voltage path around it through the secondary
protector and back though the first primary protector that fired. In this situation, the breakover diode sees the same current as the
primary arrestor. Typically, for this mechanism to occur both primary and secondary surge protectors need to have break-over
characteristics.
There are several remedies to prevent this. One is to insert a resistance of about 5 Ω in series with Tip and Ring but before the
breakover diode. The added resistance increases the voltage drop sufficiently to ensure that the second primary arrestor triggers on
large current transients. Small transients can be absorbed by the breakover diode. If a resistor is used, it must be capable of
withstanding the worse-case surge. If it has suitable fuse characteristics and is flame proof, then it can be used as an inexpensive
slow-blow fuse for protection against line cross. Contact Silicon Labs for possible resistor types. Another remedy is to use a larger
secondary breakover diode.
What surge capacity, then, does a breakover diode need to withstand for low field return rates? Experience shows that a DAA that
survives an FCC part 68 Type-B surge provides good field immunity against most lightning surges over the life of the product. This
surge specifies a 1 kV peak produced by discharging a 20 µF source capacitor with about 40 Ω of resistance for limiting current. Into
a break-over diode, this produces a peak current of about 25A. Several vendors produce breakover diodes rated to survive this test.
Although the designer can use more robust components to survive a FCC part 68 Type-A surge, (800V, 100A), the added expense is
probably not warranted. Furthermore, a Type-A surge only requires a safe failure mode, not continued product operation. Generally,
lightning surges that produce differential surges of 100A are likely to cause extensive damage to a wide variety of electrical devices
in the house. As pointed out earlier, the telephone line resistance limits the peak current. Long lines will tend to have higher-voltage
and more numerous surges, but the increased resistance helps limit the surge current.
The IA3222 Line Side has a smart power-limiting hook control circuit that prevents damage to the hook switch; either during high
voltage surges or even if continuous high voltage is present on the line. The chip senses both line voltage and line current. If the line
voltage exceeds 100V or the loop current exceeds 170mA, the hook switch turns off to prevent excessive power dissipation in the
main hook transistors. This prevents thermal overstress damage as might occur during ringing peaks, from any surge voltage, or by
connecting the DAA to a digital PBX supply with no current limit.
The digital PBX issue has been a major return rate problem on modem DAAs especially for laptop computers. Digital PBX phone
systems normally provide 24 to 50V to power smart phones. This power may be current limited to 1A or even more, only to prevent a
fire hazard. Some systems provide power, control and audio digital signaling down the normal Tip and Ring pair. If a regular
telephone device is plugged into these lines, it may damage the DAA, since normal DAAs only expect up to 120 mA of loop current.
Power-Line Cross
A power-line cross happens when a power line erroneously gets connected to the phone line. All DAAs provide isolation protection
against common-mode power line cross, but may not provide protection against differential line cross (full power applied between tip
and ring). Most regulatory standards only require protection against common-mode power-line AC voltages and not differential power
line voltages. Line cross is a much rarer event than lightning surges. Over the life of the product, this typically has less than a 1%
chance of happening.
A line cross can occur from the user side or from the telephone system side. If the chassis of a telephone product somehow gets
shorted to one side of the AC power line, then the DAA isolation protects telephone-company technicians and equipment from
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