PRELIMINARY

CPC75282

R00E

PRELIMINARY

13

2.3 Switch Logic

2.3.1 Start-up

threshold, the smart logic places the control logic to

the switch control inputs must be properly conditioned.

2.3.2 Switch Timing

When switching from the ringing state to the idle/talk

state, the CPC75282 provides the ability to control the

release timing of the ringing switches, SW3 and SW4,

relative to the state of the switches, SW1 and SW2,

using simple logic inputs. The two available

techniques are referred to as make-before-break and

break-before-make operation. When the break switch

contacts of SW1 and SW2 are closed (made) before

the ringing 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 ringing contacts of SW3

and SW4 are opened (broken) before the switch

contacts of SW1 and SW2 are closed (made).

With the CPC75282, make-before-break and

break-before-make operations can easily be

accomplished by applying the proper sequence of

logic-level inputs to the device.

The logic sequences for either mode of operation are

given in “Make-Before-Break Operation Logic

Table (Ringing to Talk Transition)” on page 13 and

“Break-Before-Make Ringing to Talk Transition

Logic Sequence CPC7592xA/B” on page 14. Logic

states and explanations are shown in “Truth Tables”

on page 11.

2.3.3 Make-Before-Break Operation

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

inputs from the ringing state directly to the idle/talk

state. Application of the idle/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 CPC75282

protection circuitry thresholds will be diverted away

from the SLIC.

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

State

(CFG=0, P3=0)

P2

P1

Timing

Break

Switches

Ringing

Return

Switch

Ringing

Switch

Test

Switches

Ringing

1

0

01

-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

Idle/Talk

0

0

Zero-cross current has occurred

On

Off

Off

Off