CPC7594

14

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R03

Make-Before-Break Ringing to Talk Transition Logic Sequence

2.3.4 Break-Before-Make Operation

Break-before-make operation of the CPC7594 can be

achieved using two different techniques.

“Break-Before-Make Ringing to Talk Transition Logic

Sequence” on page 14.

1.

At the end of the ringing state apply the all off

state (1,1). This releases the ringing return

switch (SW3) while the ringing switch (SW4)

remains on, waiting for the next zero current

event.

2.

Hold the all off state for at least one-half of a

ringing cycle to assure that a zero crossing event

occurs and that SW4, the ringing switch, has

opened.

3.

Apply inputs for the next desired state. For the

talk state, the inputs would be (0,0).

Break-before-make operation occurs when the ringing

switches open before the break switches SW1 and

SW2 close.

Break-Before-Make Ringing to Talk Transition Logic Sequence

2.3.5 Alternate Break-Before-Make Operation

The alternate break-before-make technique is

available for all versions of the CPC7594. As shown in

“CPC7594xA and CPC7594xB Truth Table” on

page 11 and “CPC7594xC Truth Table” on page 11,

switches when pulled to a logic low. Although logically

disabled, an active ringing switch (SW4) will remain

closed until the next zero crossing current event.

As shown in the table “Alternate Break-Before-Make

Ringing to Talk Transition Logic Sequence” on

page 15, this operation is similar to the one shown in

“Alternate Break-Before-Make Operation” on page 14,

except in the method used to select the all off state,

reconfigured for the talk state.

State

LATCH

Timing

Break

Switches

Ringing

Return

Switch

(SW3)

Ringing

Switch

(SW4)

Test

Switches

Ringing

1

0

0Z

-Off

On

On

Off

Make-

before-

break

00

SW4 waiting for next zero-current crossing to

turn off. Maximum time is one-half of the

ringing cycle. In this transition state current

limited by the dc break switch current limit

value will be sourced from the ring node of

the SLIC.

On

Off

On

Off

Talk

0

0

Zero-cross current has occurred

On

Off

Off

Off

State

LATCH

Timing

Break

Switches

Ringing

Return

Switch

(SW3)

Ringing

Switch

(SW4)

Test

Switches

Ringing

1

0

0Z

-Off

On

On

Off

All-Off

1

1

Hold this state for at least one-half of the

ringing cycle. SW4 waiting for zero current to

turn off.

Off

Off

On

Off

Break-

Before-

Make

11

Zero current has occurred.

SW4 has opened

Off

Off

Off

Off

Talk

0

0

Break switches close.

On

Off

Off

Off