CPC5622 datasheet(10/18 Pages) IXYS

10 / 18 page

INTEGRATED CIRCUITS DIVISION

CPC5622

www.ixysic.com

R03

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 detect signalling reception

• Caller ID signalling reception

• Switch hook

LITELINK can accommodate specific application

features without sacrificing basic functionality or

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

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) for 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.

With OH high, LITELINK is on-hook and ready to

make or receive a call. Also while on-hook,

LITELINK’s ringing detector and CID amplifiers are

both active.

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 not asserted), an internal

multiplexer engages the snoop circuitry. This circuit

simultaneously monitors the telephone line for two

conditions; incoming ringing signal and caller ID data

bursts.

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+ input pins of the LITELINK

while coupling AC signals to the snoop amplifier. The

snoop circuit “snoops” the telephone line continuously

while drawing no dc current. In the LITELINK, the

incoming ringing signals are compared to a reference

level. When the ringing signal exceeds the preset

threshold, the internal comparators generate the

RING and RING2 signals which are output from

LITELINK at pins 9 and 10, respectively. Selection of

which output to use is dependent upon the support

logic responsible for monitoring and filtering the

ringing detect signals. To reduce or eliminate false

ringing detects this signal should be digitally filtered

and qualified by the system as a valid ringing signal. A

logic low output on RING or RING2 indicates that the

LITELINK ringing signal detect threshold has been

exceeded. In the absence of any incoming ac signal

the RING and RING2 outputs are held high.

The CPC5622 RING output signal is generated by a

half-wave ringing detector while the RING2 output is

generated by a full-wave ringing detector. A half-wave

ringing detector’s output frequency follows the

frequency of the incoming ringing signal from the

Central Office (CO) while a full-wave ringing detector’s

output frequency is twice that of the incoming signal.

Because RING is the output of a half-wave detector, it

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