CPC7691

12

PRELIMINARY

R00E

Make-Before-Break Ringing to Talk Transition Logic Sequence

2.3.4 Break-Before-Make Operation

Break-before-make ringing switch release timing is

when pulled to a logic low. Although logically disabled,

an active (closed) ringing switch (SW4) will remain

closed until the next current zero crossing event. This

operational sequence is shown below in the

“Break-Before-Make Ringing to Talk Transition Logic

Sequence” on page 12.

1.

This opens the ringing return switch (SW3) and

prevents any other switches from closing.

2.

the ringing cycle period to allow sufficient time for

a zero crossing current event to occur and for the

circuit to enter the break before make state.

3.

input for the talk state (logic low).

4.

activate the break switches.

states are “0” which overrides the logic input pins and

forces an all-off state and “Z” which allows normal

switch control via the logic input pins. This requires the

use of an open-collector or open-drain type buffer.

Break-Before-Make Ringing to Talk Transition Logic Sequence

Logic states and explanations are provided in the “Truth Table” on page 9.

2.4 Data Latch

The CPC7691 has an integrated transparent data

latch. The latch enable operation is controlled by TTL

logic input levels at the LATCH pin. Data input to the

the data latch are internal nodes used for state control.

When the LATCH enable control pin is at logic 0 the

control signal flows directly through the data latch to

will be reflected by a change in switch state.

State

Latch

Timing

Break

Switches

Ringing

Return

Switch

(SW3)

Ringing

Switch

(SW4)

Ringing

1

0Z

-Off

On

On

Make-

Before-

Break

0

SW4 waiting for next zero-current crossing to

turn off. Maximum time is one-half of the ringing

cycle. In this transition state, current that is

limited to the dc break switch current limit value

will be sourced from the ring node of the SLIC.

On

Off

On

Talk

0

Zero-cross current has occurred

On

Off

Off

State

Latch

Timing

Break

Switches

Ringing

Return

Switch

(SW3)

Ringing

Switch

(SW4)

Ringing

1

0

Z-

Off

On

On

All-off

1

0

Hold this state for one-half of the ringing cycle.

SW4 waiting for zero current to turn off.

Off

Off

On

All-off

0

Zero current has occurred. SW4 has opened

Off

Off

Off

Talk

0

Z

Close break switches

On

Off

Off