CPC5620 Datasheet, PDF (10/18 Pages) Clare, Inc. – LITELINK III Phone Line Interface IC (DAA)

INTEGRATED CIRCUITS DIVISION
CPC5620/CPC5621
3. Using LITELINK
As a full-featured telephone line interface, LITELINK
performs the following functions:
• DC termination and V/I slope control
• AC impedance control
• 2-wire to 4-wire conversion (hybrid)
• Current limiting
• Ringing signal reception
• Caller ID signaling reception
• Switch hook
LITELINK can accommodate specific application
features without sacrificing basic functionality and
performance. Application features include, but are not
limited to:
• High transmit power operation
• Pulse dialing
• Ground start
• Loop start
• Parallel telephone off-hook detection (line intrusion)
• Battery reversal detection
• Line presence detection
• World-wide programmable operation
With OH high, LITELINK is on-hook and ready to
make or receive a call. While on-hook, the CID control
is used to select between passing the caller-ID tones
from Tip and Ring to the RX+ and RX- outputs and the
ringing detect function. Setting CID to a logic low
enables the CID path while placing CID to a logic high
configures the LITELINK to detect ringing.
Asserting OH low causes LITELINK to answer or
originate a call by entering the off-hook state. In the
off-hook state, loop current flows through LITELINK.
3.2 On-hook Operation: OH=1
The LITELINK application circuit leakage current is
less than 10 A with 100 V across ring and tip,
equivalent to greater than 10 M on-hook resistance.
3.2.1 Ringing Signal Reception via the
Snoop Circuit
In the on-hook state (OH and CID not asserted), an
internal multiplexer turns on the snoop circuit. This
circuit monitors the telephone line for two conditions;
an incoming ring signal, and caller ID data bursts.
This section of the data sheet describes LITELINK
operation in standard configuration for usual
operation. IXYS Integrated Circuits Division offers
additional application information on-line (see Section 5
on page 14). These include information on the following
topics:
• Circuit isolation considerations
• Optimizing LITELINK performance
• Data Access Arrangement architecture
• LITELINK circuit descriptions
• Surge protection
• EMI considerations
Other specific application materials are also
referenced in this section as appropriate.
3.1 Switch Hook Control (On-hook
and Off-hook States)
LITELINK operates in one of two conditions, on-hook
and off-hook. In the on-hook condition the telephone
line is available for calls. In the off-hook condition the
telephone line is engaged. The OH control input is
used to place LITELINK in one of these two states.
Refer to the application schematic diagram (see Figure
2. on page 6). C7 (CSNP-) and C8 (CSNP+) provide a
high-voltage isolation barrier between the telephone
line and SNP- and SNP+ on the LITELINK while
coupling AC signals to the snoop amplifier. The snoop
circuit “snoops” the telephone line continuously while
drawing no current. In the LITELINK, ringing signals
are compared to a threshold. The comparator output
forms the RING signal output from LITELINK. This
signal must be qualified by the host system as a valid
ringing signal. A low level on RING indicates that the
LITELINK ring signal threshold has been exceeded.
For the CPC5620 (with the half-wave ring detector),
the frequency of the RING output follows the
frequency of the ringing signal from the central office
(CO), typically 20 Hz. The RING output of the
CPC5621 (with the full-wave ring detector) is twice the
ringing signal frequency.
Hysteresis is employed in the LITELINK ring detector
circuit to provide noise immunity. The set-up of the ring
detector comparator causes RING output pulses to
remain low for most of the ringing signal half-cycle.
The RING output returns high for the entire negative
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