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

CPC5620/CPC5621
3. Using LITELINK
As a full-featured telephone line interface, LITELINK
performs the following functions:
hook state, loop current flows through LITELINK and
the system is answering or placing a call.
• DC termination
• AC impedance control
• V/I slope control
3.2 On-hook Operation
• 2-wire to 4-wire conversion (hybrid)
The LITELINK application circuit leakage current is
• Current limiting
less than 10 µA with 100 V across ring and tip, equiva-
• Ring signal reception
• Caller ID signal reception
• Switch hook
y _{LITELINK can accommodate specific application fea-}
tures without sacrificing basic functionality and perfor-
r _{mance. Application features include, but are not}
limited to:
a _{• High transmit power operation}
in ^{• Pulse dialing}
• Ground start
• Loop start
• Parallel telephone off-hook detection (911 feature)
• Battery reversal detection
lim ^{• Line presence detection}
• World-wide programmable operation
This section of the data sheet describes LITELINK
operation in standard configuration for usual opera-
e tion. Clare offers additional application information on-
line (see Section 5 on page 14). These include informa-
r _{tion on the following topics:}
P ^{• Circuit isolation considerations}
lent to greater than 10 MΩ on-hook resistance.
3.2.1 Ring 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 cir-
cuit monitors the telephone line for two conditions; an
incoming ring signal, and caller ID data bursts.
Refer to the application schematic diagram (see Figure
3 on page 6). C7 (C_SNP-) and C8 (C_SNP+) provide a
high-voltage isolation barrier between the telephone
line and SNP- and SNP+ on the LITELINK while cou-
pling AC signals to the snoop amplifier. The snoop cir-
cuit “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 sig-
nal 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 fre-
• Optimizing LITELINK performance
quency of the ringing signal from the central office
• Data Access Arrangement architecture
(CO), typically 20 Hz. The RING output of the
• LITELINK circuit descriptions
CPC5621 (with the full-wave ring detector) is twice the
• Surge protection
ringing signal frequency.
• EMI considerations
Hysteresis is employed in the LITELINK ring detector
Other specific application materials are also refer-
enced in this section as appropriate.
circuit to provide noise immunity. The setup 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
half-cycle of the ringing signal for the CPC5620. For
3.1 Switch Hook Control (On-hook
and Off-hook States)
the CPC5621, the RING output returns high for a short
period near the zero-crossing of the ringing signal
before returning low during the positive half-cycle. For
LITELINK operates in one of two conditions, on-hook
both the CPC5620 and CPC5621, the RING output
and off-hook. In the on-hook condition the telephone
remains high between ringing signal bursts.
line is available for calls. In the off-hook condition the
telephone line is engaged. Use the OH control input to
The ring detection threshold depends on the values of
place LITELINK in one of these two states. With OH
high, LITELINK is on-hook and ready to make or
receive a call. The snoop circuit is enabled. Assert OH
low to place LITELINK in the off-hook state. In the off-
R3 (R_SNPD), R6 (R_SNP-), R7 (R_SNP+), C7 (C_SNP-), and
C8 (C_SNP+). The values for these components shown
in the typical application circuits are recommended for
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