CPC7592 Datasheet, PDF (14/19 Pages) Clare, Inc. – Line Card Access Switch

INTEGRATED CIRCUITS DIVISION
CPC7592
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 CPC7592xA/B
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 Break-Before-Make Operation - All Versions
The second break-before-make method for the
CPC7592xA/B is also the only method available for
the CPC7592xC. As shown in “CPC7592xA and
CPC7592xB Truth Table” on page 10 and “CPC7592xC Truth
Table” on page 10, the bi-directional T_SD interface
disables all of the CPC7592 switches when pulled to a
logic low. Although logically disabled, an active
(closed) ringing switch (SW4) will remain closed until
the next zero crossing current event.
When using T_SD as an input, the two recommended
states are “0” which overrides the logic input pins and
forces 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.
As shown in the table “Break-Before-Make Ringing to Talk
Transition Logic Sequence for all Versions” on page 15, this
operation is similar to the one shown in
“Break-Before-Make Operation - All Versions” 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.
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 and
IN_TEST inputs to the talk state (0, 0).
4. Release T_SD, allowing the internal pull-up to
activate the break switches.
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