CPC7593

R05

www.ixysic.com

17

The logic sequences for either mode of operation are

given in “Make-Before-Break Operation Logic Table

(Ringing to Talk Transition)” on page 17,

“Break-Before-Make Operation Logic Table (Ringing to Talk

Transition)” on page 18 and “Alternate Break-Before-Make

Operation Logic Table (Ringing to Talk Transition)” on

page 19. Logic states and explanations are shown in

“Truth Tables” on page 14.

2.3.3 Make-Before-Break Operation

To use make-before-break operation, change the logic

inputs from the ringing state directly to the talk state.

Application of the talk state opens the ringing return

switch, SW3, as the break switches SW1 and SW2

close. The ringing switch, SW4, remains closed until

the next zero-crossing of the ringing current. While in

the make-before-break state, ringing potentials in

excess of the CPC7593 protection circuitry thresholds

will be diverted away from the SLIC.

2.3.4 Make-Before-Break Operation Logic Table (Ringing to Talk Transition)

2.3.5 Break-Before-Make Operation

Break-before-make operation of the CPC7593 can be

achieved using two different techniques.

“Break-Before-Make Operation Logic Table (Ringing to Talk

Transition)” on page 18.

1.

At the end of the ringing state apply the all-off

state (1,0,1). This releases the ringing return

switch (SW3) while the ringing switch 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 the ringing switch (SW4) has

opened.

3.

Apply inputs for the next desired state. For the

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

Break-before-make operation occurs when the ringing

switch opens before the break switches SW1 and

SW2 close.

State

Latch

Timing

Break

Switches

Ringing

Return

Switch

(SW3)

Ringing

Switch

(SW4)

Test

Switches

Ringing

1

0

0

0Z

-Off

On

On

Off

Make-

Before-

Break

00

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

break switch dc current limit

value will be sourced from the

ring node of the SLIC.

On

Off

On

Off

Talk

0

0

0

Zero-cross current has occurred

On

Off

Off

Off