SI3015-FS Silicon Laboratories Inc, SI3015-FS Datasheet - Page 80

• Manufacturer Part Number: SI3015-FS
• Description: SI2400 ISOMODEM LINE-SIDE
• Manufacturer: Silicon Laboratories Inc

Specifications of SI3015-FS

• Data Format: V.90
• Interface: Serial
• Voltage - Supply: 3.3 V ~ 5 V
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Baud Rates: -

Si2400
selected with SF5[4] (ACT).
ACT = 0b is a real, nominal 600 Ω termination which
satisfies the impedance requirements of FCC part 68,
JATE, and other countries. This real impedance is set
by circuitry internal to the Si2400 chipset as well as the
resistor R2 connected to the Si3015 REXT pin.
ACT = 1b is a complex impedance which satisfies the
impedance requirements of Australia, New Zealand,
South Africa, CTR21 and some European NET4
countries such as the UK and Germany. This complex
impedance is set by circuitry internal to the Si2400
chipset as well as the network connected to the Si3015
REXT2 pin.
Ringer Impedance
The ring detector in a typical DAA is ac coupled to the
line with a large, 1 µ F, 250 V decoupling capacitor. The
ring detector on the Si2400 is also capacitively coupled
to the line, but it is designed to use smaller, less
expensive 560 pF capacitors. Inherently, this network
produces a very high ringer impedance to the line on
the order of 800 to 900 k Ω . This value is acceptable for
most countries, including FCC and CTR21.
Several countries, including Poland, South Africa and
South Korea, require a maximum ringer impedance. For
Poland, South Africa and South Korea, the maximum
ringer impedance specification can be met with an
internally synthesized impedance by setting SF5[1] (RZ)
= 1b.
DTMF Dialing
In CTR21 dc termination mode, set SF6[2] (DIAL) = 1b
during DTMF dialing if SDB (LVCS) ≤ 11. Setting this bit
increases headroom for large signals. This bit should
only be used during dialing and if SDB (LVCS) < 11.
In Japan dc termination mode (SF5[3:2] (DCT) = 01b),
the ISOmodem attenuates the transmit output by 1.7 dB
to meet headroom requirements. Similarly, in Low
Voltage mode (DCT = 00b), the ISOmodem attenuates
the transmit output by 4 dB. However, when DTMF
dialing is desired in these modes, this attenuation must
be removed. This is achieved by entering the FCC dc
termination mode and setting SF6[3] (FJM) = 1b or
SF6[0] (FLVM) = 1. When in the FCC dc termination
modes, these bits will enable the respective lower loop
current termination modes without the associated
transmit attenuation. Increased distortion may be
observed, which is acceptable during DTMF dialing.
After DTMF dialing is complete, the attenuation should
be enabled by returning to either the Japan dc
termination mode (DCT = 01b) or the Low Voltage
termination mode (DCT = 00b). SF6[3] (FJM) and
SF6[0] (FLVM) have no effect in any other termination
80
Rev. 1.1
mode other than the FCC dc termination mode.
Pulse Dialing
Pulse dialing is accomplished by going off and on hook
to generate make and break pulses. The nominal rate is
10 pulses per second. Some countries have very tight
specifications for pulse fidelity, including make and
break times, make resistance, and rise and fall times. In
a traditional solid-state dc holding circuit, there are a
number of issues in meeting these requirements.
The Si2400 dc holding circuit has active control of the
on-hook and off-hook transients to maintain pulse
dialing fidelity.
Spark quenching requirements in countries such as
Italy, 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
the sudden decrease in current through the loop when
going on-hook. The traditional way of dealing with this
problem is to put a parallel RC shunt across the
hookswitch relay. The capacitor is large (~1 uF, 250 V)
and expensive. In the Si2400, SF5[6:5] (OHS) can be
used to slowly ramp down the loop current to pass these
tests without requiring additional components.
Billing Tone Detection
“Billing tones” or “metering pulses” generated by the
central office can cause modem connection difficulties.
The billing tone is typically either 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 Si2400 chipset can provide feedback when
a billing tone occurs and when it ends.
Billing tone detection is enabled by setting SF1[7]
(BTE) = 1b. Billing tones less than 1.1 V
will be filtered out by the low pass digital filter on the
Si2400. SF9[1] (ROV) is set when a line signal is
greater than 1.1 V
condition. SF9[3] (BTD) is set when a line signal (billing
tone) is large enough to excessively reduce the line-
derived power supply of the line-side device (Si3015).
When the BTD 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 a billing tone
detection. When the OVL bit returns to zero, indicating
that the billing tone has passed, the BTE bit should be
written to zero to return the dc termination to its original
state. It will take approximately one second to return to
normal dc operating conditions. The BTD and ROV bits
are sticky, and they must be written to zero to be reset.
PK
, indicating a receive overload
PK
on the line