CPC5620/CPC5621

10

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R05

3. Using LITELINK

As a full-featured telephone line interface, LITELINK

performs the following functions:

LITELINK can accommodate specific application

features without sacrificing basic functionality and

performance. Application features include, but are not

limited to:

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:

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. 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.

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