CPC7593 Datasheet, PDF (17/24 Pages) Clare, Inc. – Line Card Access Switch

INTEGRATED CIRCUITS DIVISION
CPC7593
The logic sequences for either mode of operation are
given in “Make-Before-Break Operation Logic Table
(Ringing to Talk Transition)” on page 17,
“Break-Before-Make Operation Logic Table (Ringing to Talk
Transition)” on page 18 and “Alternate Break-Before-Make
Operation Logic Table (Ringing to Talk Transition)” on
page 19. Logic states and explanations are shown in
“Truth Tables” on page 14.
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 CPC7593 protection circuitry thresholds
will be diverted away from the SLIC.
2.3.4 Make-Before-Break Operation Logic Table (Ringing to Talk Transition)
State IN_RINGING IN_TESTin IN_TESTout Latch
Ringing
1
0
0
Make-
Before-
0
0
0
0
Break
Talk
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 that is limited to the
On
Off
On
Off
break switch dc current limit
value will be sourced from the
ring node of the SLIC.
Zero-cross current has occurred On
Off
Off
Off
2.3.5 Break-Before-Make Operation
Break-before-make operation of the CPC7593 can be
achieved using two different techniques.
The first method uses manipulation of the (IN_RINGING,
IN_TESTin, IN_TESTout) logic inputs as shown in
“Break-Before-Make Operation Logic Table (Ringing to Talk
Transition)” on page 18.
1. At the end of the ringing state apply the all-off
state (1,0,1). This releases the ringing return
switch (SW3) while the ringing switch 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 the ringing switch (SW4) has
opened.
3. Apply inputs for the next desired state. For the
talk state, the inputs would be (0,0,0).
Break-before-make operation occurs when the ringing
switch opens before the break switches SW1 and
SW2 close.
R05
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