CPC7595

R02

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17

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

2.3.4 Break-Before-Make Operation

Break-before-make operation of the CPC7595 can be

achieved using two different techniques.

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

Transition)” on page 17.

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.

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

2.3.5 Alternate Break-Before-Make Operation

The second break-before-make method is also

available for use with all versions of the CPC7595. As

shown in “Truth Table for CPC7595xA and CPC7595xB” on

page 14 and “Truth Table for CPC7595xC” on page 14, the

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

State

Latch

Timing

Break

Switches

Ringing

Return

Switch

(SW3)

Ringing

Switch

(SW4)

Test

Switches

Ringing

1

0

0

0Z

-Off

On

On

Off

10

1

Hold this state for at least

one-half of ringing cycle.

SW4 waiting for zero current

to turn off.

Off

Off

On

Off

Break-

Before-

10

1

Zero current has occurred.

SW4 has opened

Off

Off

Off

Off

Talk

0

0

0

Break switches close.

On

Off

Off

Off

* For the CPC7595xA/B versions the input pattern (1,1,1) may also be used for the all-off state.