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R01

CPC7691

This monitor function performs properly if the

CPC7691 and SLIC share a common battery supply

origin. Otherwise, if battery is lost to the CPC7691 but

the internal protection circuitry.

2.7 Ringing to Talk State Switch Timing

The CPC7691 provides, when switching from the

Ringing state to the Talk state, the ability to control the

release timing of the ringing switches, SW3 and SW4,

relative to the activation of the break switches, SW1

and SW2, using simple TTL logic-level inputs. The two

available techniques are referred to as

make-before-break and break-before-make. When the

switch contacts of SW1 and SW2 are closed (made)

before the switch contacts of SW3 and SW4 are

opened (broken), this is referred to as

make-before-break operation. Break-before-make

operation occurs when the contacts of SW3 and SW4

are opened (broken) before the switch contacts of

SW1 and SW2 are closed (made). With the CPC7691,

make-before-break and break-before-make operations

can easily be accomplished by applying the proper

sequence of inputs to the device.

2.7.1 Make-Before-Break Operation

To use make-before-break operation, change

state. Assertion 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 CPC7691 protection

circuitry thresholds will be diverted away from the

SLIC. This operational sequence is shown below in

the Ringing to Talk Logic Sequence: Make-Before-Break.

Ringing to Talk Logic Sequence: Make-Before-Break

2.7.2 Break-Before-Make Operation

Break-before-make switch timing is performed via the

disable all of the CPC7691 switches when pulled to a

logic low. Although logically disabled, an active

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

the next zero crossing current event. This operational

sequence is shown below in the Ringing to Talk Logic

Sequence: Break-Before-Make.

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 inputs while

forcing 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.

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