CPC7593 Datasheet, PDF (18/24 Pages) Clare, Inc. – Line Card Access Switch

INTEGRATED CIRCUITS DIVISION
CPC7593
2.3.6 Break-Before-Make Operation Logic Table (Ringing to Talk Transition)
State IN_RINGING IN_TESTin IN_TESTout Latch
T_SD
Timing
Break
Switches
Ringing
Return
Switch
(SW3)
Ringing
Switch
(SW4)
Test
Switches
Ringing
1
0
0
-
Off
On
On
Off
All-off ^*
1
0
1
Break-
Before-
1
0
1
Make ^*
Hold this state for at least
one-half of ringing cycle. SW4
waiting for zero current to turn
Off
Off
On
Off
0
Z
off.
Zero current has occurred. SW4
has opened
Off
Off
Off
Off
Talk
0
0
0
Break switches close.
On
Off
Off
Off
* For the CPC7593xA/B versions the input pattern (1,1,1) may also be used for the all-off state.
2.3.7 Alternate Break-Before-Make Operation
The second break-before-make method is also
available for use with all versions of the CPC7593. As
shown in “Truth Table for CPC7593xA and CPC7593xB” on
page 14 and “Truth Table for CPC7593xC and CPC7593xD”
on page 14, the bi-directional T_SD interface disables all
of the CPC7593 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.
When using T_SD 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.
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 IN_RINGING,
IN_TESTin and IN_TESTout inputs are reconfigured for the
talk state.
1. Pull T_SD to a logic low to end the ringing state.
This opens the ringing return switch (SW3) and
prevents any other switches from closing.
2. Keep T_SD 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.
3. During the T_SD low period, set the IN_RINGING,
IN_TESTin and IN_TESTout inputs to the talk state
(0,0,0).
4. Release T_SD allowing the internal pull-up to
activate the break switches.
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