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

INTEGRATED CIRCUITS DIVISION
CPC7594
The logic sequences for either mode of operation are
provided in “Make-Before-Break Ringing to Talk Transition
Logic Sequence” on page 14, “Break-Before-Make Ringing
to Talk Transition Logic Sequence” on page 15, and
“Alternate Break-Before-Make Ringing to Talk Transition
Logic Sequence” on page 15. Logic states and input
control settings are provided in “CPC7594xA and
CPC7594xB Truth Table” on page 11 and “CPC7594xC Truth
Table” on page 11.
2.3.3 Make-Before-Break Operation
To use make-before-break operation, change the logic
inputs from the ringing state directly to the talk state.
Application of the talk state opens the ringing return
switch, SW3, as the break switches SW1 and SW2
close. The ringing switch, SW4, remains closed until
the next zero-crossing of the ringing current. While in
the make-before-break state, ringing potentials in
excess of the CPC7594 protection circuitry thresholds
will be diverted away from the SLIC.
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 15.
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.
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