CPC7595 datasheet(18/25 Pages) IXYS

18 / 25 page

INTEGRATED CIRCUITS DIVISION

www.ixysic.com

R03

CPC7595

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

bidirectional TSD interface disables all of the CPC7595

switches when pulled to a logic low. Although logically

disabled, an active (closed) ringing switch (SW4) will

remain closed until the next current zero crossing

event.

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

Logic Table (Ringing to Talk Transition)” on page 18, this

operation is similar to the one shown in “Alternate

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

Transition)” on page 19, except in the method used to

select the all-off state and when the INRINGING,

INTESTin and INTESTout inputs are reconfigured for the

talk state.

Pull TSD to a logic low to end the ringing state.

This opens the ringing return switch (SW3) and

prevents any other switches from closing.

Keep TSD low for at least one-half the duration of

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.

During the TSD low period, set the INRINGING,

INTESTin and INTESTout inputs to the talk state

(0,0,0).

Release TSD allowing the internal pull-up to

activate the break switches.

When using TSD as an input, the two recommended

states are “0” which over rides logic input pins and

forces an all-off state and “Z” which allows switch

control via the logic input pins. This requires the use of

an open-collector or open-drain type buffer.

State

INRINGING INTESTin INTESTout

Latch

TSD

Timing

Break

Switches

Ringing

Return

Switch

(SW3)

Ringing

Switch

(SW4)

Test

Switches

Ringing

-Off

Off

All-off *

Hold this state for at least

one-half of ringing cycle.

SW4 waiting for zero current

to turn off.

Off

Break-

Before-

Make *

Zero current has occurred.

SW4 has opened

Off

Talk

Break switches close.

Off

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

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