CPC7594 Datasheet, PDF (14/20 Pages) Clare, Inc. – Line Card Access Switch

CPC7594
State
Ringing
Make-
before-
break
Talk
IN_RINGING
1
0
0
Make-Before-Break Ringing to Talk Transition Logic Sequence
IN_TEST LATCH
0
0
0
0
T_SD
Timing
Break
Switches
Ringing
Return
Switch
(SW3)
Ringing
Switch
(SW4)
Test
Switches
-
Off
On
On
Off
SW4 waiting for next zero-current crossing to
turn off. Maximum time is one-half of the
Z
ringing cycle. In this transition state current
limited by the dc break switch current limit
On
Off
On
Off
value will be sourced from the ring node of
the SLIC.
Zero-cross current has occurred
On
Off
Off
Off
2.3.4 Break-Before-Make Operation
Break-before-make operation of the CPC7594 can be
achieved using two different techniques.
The first method uses manipulation of the IN_RINGING
and IN_TEST logic inputs as shown in
“Break-Before-Make Ringing to Talk Transition Logic
Sequence” on page 14.
1. At the end of the ringing state apply the all off
state (1,1). This releases the ringing return
switch (SW3) while the ringing switch (SW4)
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 SW4, the ringing switch, has
opened.
3. Apply inputs for the next desired state. For the
talk state, the inputs would be (0,0).
Break-before-make operation occurs when the ringing
switches open before the break switches SW1 and
SW2 close.
State
Ringing
All-Off
Break-
Before-
Make
Talk
IN_RINGING
1
1
1
0
Break-Before-Make Ringing to Talk Transition Logic Sequence
IN_TEST LATCH
0
1
0
1
T_SD
Timing
Break
Switches
Ringing
Return
Switch
(SW3)
Ringing
Switch
(SW4)
Test
Switches
-
Off
On
On
Off
Hold this state for at least one-half of the
ringing cycle. SW4 waiting for zero current to Off
Off
On
Off
turn off.
Z
Zero current has occurred.
SW4 has opened
Off
Off
Off
Off
0
Break switches close.
On
Off
Off
Off
2.3.5 Alternate Break-Before-Make Operation
The alternate break-before-make technique is
available for all versions of the CPC7594. As shown in
“CPC7594xA and CPC7594xB Truth Table” on
page 11 and “CPC7594xC Truth Table” on page 11,
the bi-directional T_SD interface disables all of the
switches when pulled to a logic low. Although logically
disabled, an active ringing switch (SW4) will remain
closed until the next zero crossing current event.
As shown in the table “Alternate Break-Before-Make
Ringing to Talk Transition Logic Sequence” on
page 15, this operation is similar to the one shown in
“Alternate Break-Before-Make Operation” on page 14,
except in the method used to select the all off state,
and in when the IN_RINGING and IN_TEST inputs are
reconfigured for the talk state.
14
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