SI2493-C-FT Silicon Laboratories Inc, SI2493-C-FT Datasheet - Page 16

• Manufacturer Part Number: SI2493-C-FT
• Description: 56 KBPS, V.92 ISOMODEM SYSTEM-SIDE - LEAD-FREE TSSOP 0 TO 7
• Manufacturer: Silicon Laboratories Inc

Specifications of SI2493-C-FT

• Mfg Application Notes: SI2493/57/34/15/04, Appl Note AN93
• Data Format: V.21, V.22, V.23, V.29, V.32, V.34, V.90, V.92, Bell 103, Bell 212A
• Baud Rates: 56k
• Interface: Parallel
• Voltage - Supply: 3 V ~ 3.6 V
• Mounting Type: Surface Mount
• Package / Case: 24-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AN93
2.2.13. Ringer Impedance and Threshold
The ring detector in many DAAs is ac coupled to the line
with a large 1 µF, 250 V decoupling capacitor. The ring
detector on the Si2493/57/34/15/04 is resistively
coupled to the line. This produces a high ringer
impedance to the line of approximately 20 MΩ to meet
the majority of country PTT specifications, including
FCC and TBR21.
Several countries, including Poland, South Africa, and
Slovenia, require a maximum ringer impedance that can
be met with an internally synthesized impedance by
setting the RZ bit (Register 67, bit 1).
Some
differently. The RT bit (Register U67, bit 0) selects
between two different ringer thresholds: 15 V ±10% and
21.5 V ±10%. These two settings satisfy ringer
threshold requirements worldwide. The thresholds are
set so that a ring signal is guaranteed to be detected
above the maximum and not detected below the
minimum.
2.2.14. Pulse Dialing and Spark Quenching
Pulse dialing results from going off- and on-hook to
generate make and break pulses. The nominal rate is
10 pulses per second. Some countries have strict
specifications for pulse fidelity that include make and
break times, make resistance, and rise and fall times. In
a traditional, solid-state dc holding circuit, there are
many problems in meeting these requirements.
The Si2493/57/34/15/04 dc holding circuit actively
controls the on-hook and off-hook transients to maintain
pulse dialing fidelity.
Spark quenching requirements in countries, such as
Italy, the Netherlands, South Africa, and Australia, deal
with the on-hook transition during pulse dialing. These
tests provide an inductive dc feed resulting in a large
voltage spike. This spike is caused by the line
inductance and sudden decrease in current through the
loop when going on-hook. The traditional solution to the
problem is to put a parallel resistive capacitor (RC)
shunt across the hookswitch relay. However, the
capacitor required is large (~1 µF, 250 V) and relatively
16
Table 5. AC Termination Settings for the Si3018
ACT[3:0]
0000
0100
0011
1111
countries
600 Ω
220 Ω + (820 Ω || 120 nF) and 220 Ω +
(820 Ω || 115 nF)
370 Ω + (620 Ω || 310 nF)
Global complex impedance
Line-Side Device
also
AC Termination
specify
ringer
thresholds
Rev. 0.9
expensive. In the Si2493/57/34/15/04, loop current can
be controlled to achieve three distinct on-hook speeds
to pass spark quenching tests without additional BOM
components. Through settings of two bits in two
registers, OHS (Register U67, bit 6) and OHS2
(Register U62, bit 8), a slow ramp-down of loop current,
which induces a delay between the time the OH bit is
cleared and the time the DAA actually goes on-hook,
can be achieved .
2.2.15. Billing Tone Detection
“Billing tones” or “metering pulses” generated by the
central office can cause modem connection difficulties.
The billing tone is typically a 12 kHz or 16 kHz signal
and is sometimes used in Germany, Switzerland, and
South Africa. Depending on line conditions, the billing
tone may be large enough to cause major modem
errors. The Si2493/57/34/15/04 chipset can provide
feedback when a billing tone occurs and when it ends.
Billing tone detection is enabled by setting the BTE bit
(U68, bit 2). Billing tones less than 1.1 V
are filtered out by the low-pass digital filter on the
Si2493/57/34/15/04. The ROV bit (U68, bit 1) is set
when a line signal is greater than 1.1 V
receive overload condition. The BTD bit is set when a
line signal (billing tone) is large enough to excessively
reduce the line-derived power supply of the line-side
device (Si3018/10). When the BTE bit is set, the dc
termination is changed to an 800 Ω dc impedance. This
ensures minimum line voltage levels even in the
presence of billing tones.
The OVL bit should be polled following billing tone
detection. When the OVL bit returns to 0, indicating that
the billing tone has passed, the BTE bit should be
written to 0 to return the dc termination to its original
state. It takes approximately 1 second to return to
normal dc operating conditions. The BTD and ROV bits
are sticky and must be written to 0 to be reset. After the
BTE, ROV, and BTD bits are cleared, the BTE bit can be
set to reenable billing tone detection.
Certain line events, such as an off-hook event on a
parallel phone or a polarity reversal, may trigger the
ROV or the BTD bits, after which the billing tone detector
must be reset. Look for multiple events before qualifying
whether billing tones are actually present.
Although the DAA remains off-hook during a billing tone
event, the received data from the line is corrupted (or a
modem disconnect or retrain may occur) in the presence
of large billing tones. To receive data through a billing
tone, an external LC filter must be added. A modem
manufacturer can provide this filter to users in the form
of a dongle that connects on the phone line before the
DAA. This keeps the manufacturer from having to
PK
PK
, indicating a
on the line