CPC7594 Datasheet, PDF (15/20 Pages) Clare, Inc. – Line Card Access Switch

INTEGRATED CIRCUITS DIVISION
CPC7594
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 15, 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.
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.
Forcing T_SD to a logic high prevents the user from
detecting a thermal shutdown condition and is
therefore not recommended.
Alternate Break-Before-Make Ringing to Talk Transition Logic Sequence
State IN_RINGING IN_TEST LATCH T_SD
Timing
Ringing
Break Return
Switches Switch
(SW3)
Ringing
Switch
(SW4)
Test
Switches
Ringing
1
0
0
Z
-
Off
On
On
Off
All-Off
1
Break-
Before-
0
Make
Hold this state for at least one-half of the
0
ringing cycle. SW4 waiting for zero
Off
Off
On
Off
X
0
current to turn off.
0
SW4 has opened
Off
Off
Off
Off
Talk
0
0
0
Z
Close Break Switches
On
Off
Off
Off
R04
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