CPC5621 datasheet(10/18 Pages) CLARE

10 / 18 page

CPC5620/CPC5621

www.clare.com

Rev. 0.E

3. Using LITELINK

As a full-featured telephone line interface, LITELINK

performs the following functions:

• DC termination

• AC impedance control

• V/I slope control

• 2-wire to 4-wire conversion (hybrid)

• Current limiting

• Ring signal reception

• Caller ID signal reception

• Switch hook

LITELINK can accommodate specific application fea-

tures without sacrificing basic functionality and perfor-

mance. Application features include, but are not

limited to:

• High transmit power operation

• Pulse dialing

• Ground start

• Loop start

• Parallel telephone off-hook detection (911 feature)

• Battery reversal detection

• Line presence detection

• World-wide programmable operation

This section of the data sheet describes LITELINK

operation in standard configuration for usual opera-

tion. Clare offers additional application information on-

line (see Section 5 on page 14). These include informa-

tion 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 refer-

enced 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. Use the OH control input to

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-

hook state, loop current flows through LITELINK and

the system is answering or placing a call.

3.2 On-hook Operation

The LITELINK application circuit leakage current is

less than 10

µA with 100 V across ring and tip, equiva-

lent to greater than 10 M

Ω 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 (CSNP-) and C8 (CSNP+) 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-

quency 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 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

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

both the CPC5620 and CPC5621, the RING output

remains high between ringing signal bursts.

The ring detection threshold depends on the values of

R3 (RSNPD), R6 (RSNP-), R7 (RSNP+), C7 (CSNP-), and

C8 (CSNP+). The values for these components shown

in the typical application circuits are recommended for

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