ia3211 integration, ia3211 Datasheet - Page 4

• Manufacturer Part Number: ia3211
• Description: Optical Silicon Daa Modem/lineside Chipset
• Manufacturer: integration

(1.25V); hence, the transmit audio interface may require a
100nF decoupling capacitance.
The series resistor value and the overall gain from the Tx audio
source and the phone line are function of the following relation:
Receive Audio Interface
A single ended reception interface is available on the IA3211.
This output can drive up to 300Ω and provides a 6dB
attenuation from the phone line. Optionally, an additional
internal operating amplifier is available to achieve 0dB
attenuation from the phone line or to provide a differential
reception outputs (see audio interface figure).
Control Interface
The IA3211 and IA3212 chipset offers the designer two
different ways of setting the on and off-hook state as well as
the snoop mode. Both modes can be controlled by either an
active high or an active low input. Although both mechanisms
are valid, active high controlled signals are the preferred
method. In any case, special attention should be paid to the
various required minimum and maximum high and low voltage
levels and currents to operate those inputs as stated in the
recommended operating conditions of the data sheet.
On-hook Operation
On-hook Monitor – Caller ID Mode
Asserting either the ONHKM input (or the inverse ONHKML
input) on the IA3211 puts the DAA into SNOOP mode or on-
hook monitor mode. This is used primarily for Caller ID
purposes. When in SNOOP mode, the DAA draws a maximum of
500µA from the telephone line. Line voltage must be at least
3.5 volts. This current is much less than what the CO would
consider going off-hook, which is usually at least 5mA. On-hook
monitoring does not violate FCC part 68 rules as long as it
happens during ringing, or when another telephone device is
off-hook on the same line.
On-hook monitoring mode is an option, which requires adding
an external RC network. This is typically a 220kΩ resistor in
series with a 4.7nF capacitor from pin 18 of the IA3212 to the
negative terminal of the bridge rectifier. When active, the AC
line impedance is roughly 220kΩ.
In a typical Caller ID application, the modem firmware will
assert one of the Snoop control lines following the first ring so
as to pass the Caller ID burst of FSK tones to the data pump for
detection.
In a Voice/FAX/Data application, a Snoop control line is
asserted during the ringing and for perhaps 15 to 60 seconds
after the telephone line is answered by an external extension
telephone (when ringing stops). The modem then listens for
Tx_Gain=140/(R+20) where R is in kΩ.
FAX or Data calling tone or DTMF sequence. If a tone is
recognized, then the modem firmware can answer the call.
This steers the FAX or Data call from the answering machine,
which initially answered the call, to the modem.
V/F Converter
In the "On-Hook" condition, the DAA appears as a very high
impedance and draws only a few microamperes of line current.
A V/F (voltage to frequency) circuit monitors the open line
voltage. This voltage measurement appears at the IA3211 at
pin 23, LSTAT, in the form of a series of pulses. Each pulse is
about 4ms wide, and the frequency of the pulses is
proportional. to the line voltage. The pulses are sent across the
barrier by pulsing the RX opto-isolator during the discharge
time of the RC circuit.
Gain of the converter is based on two external components
connected to pin 19 of the IA3212. Given the reference values
of 20MΩ and 68nF, the gain of this circuit is about 1Hz/volt.
The resistor value must not be lower than 10MΩ otherwise the
circuit will not meet FCC part 68 on-hook DC resistance
specifications. The capacitor may be varied between 10 and
100nF with resulting change in pulse width and V/F gain.
This circuit is provided to allow detection of line status without
having to go off-hook. It can be used to detect when an
extension phone goes off-hook, or if the modem is connected
to a dead line. Most modem problems are improper connection
to the line.
Due to the wide variety of other telephone equipment available,
it is not possible to reliably determine line condition by
monitoring line voltage alone. Generally, line voltages below 12
to 14 volts indicate the line is in use. Voltages above 18 to 20
volts indicate the line is available. Voltages in the 12 to 20 V
range are ambiguous. This is because telephone standards
have no maximum off-hook voltage drop recommendations for
line currents over 26mA. A common situation where a high line
voltage is encountered while the line is in use, is when a user
has inserted a zener adapter in series with their answering
telephone jack to improve answering machine cutoff. These
TIP
RING
F1250T
F1
HZ 0805 B 601R
HZ 0805 B 601R
L2
L1
-
D2
CBRHG-06
+
MMBT6520
SOT23
10
11
12
1
2
3
4
5
6
7
8
9
U1
HLDR
LEDCT
HLDCAP
HKP
HKN
N.C.1
HLFWV
LR1
LR2
N.C.2
N.C.3
C1A
Q1
IA3212
IA3211 & IA3212
ONHKMCAP
C4
27nF
SRVAN
SRVCT
VFCAP
N.C.5
N.C.4
TXAN
TXCT
C1B
Vdd
Vss
C2
TN2540
SOT89
R4
56K
24
23
22
21
20
19
18
17
16
15
14
13
Q2
R9
3.9
R12
220K
C12
4.7nF
4