CPC7591 Datasheet, PDF (12/19 Pages) Clare, Inc. – Line Card Access Switch

CPC7591
State IN_RINGING Latch
Ringing
1
Make-
Before-
0
0
Break
Talk
0
Make-Before-Break Ringing to Talk Transition Logic Sequence
Ringing
T_SD
Timing
Break Return
Switches Switch
(SW3)
-
Off
On
SW4 waiting for next zero-current crossing to
turn off. Maximum time is one-half of the ringing
Z cycle. In this transition state, current that is
On
Off
limited to the dc break switch current limit value
will be sourced from the ring node of the SLIC.
Zero-cross current has occurred
On
Off
Ringing
Switch
(SW4)
On
On
Off
2.3.4 Break-Before-Make Operation
Break-before-make ringing switch release timing is
performed via the bidirectional T_SD interface. As an
input, the T_SD can disable all of the CPC7591 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. This
operational sequence is shown below in the
“Break-Before-Make Ringing to Talk Transition Logic
Sequence” on page 12.
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, clear the IN_RINGING
input for the talk state (logic low).
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.
State IN_RINGING Latch
Ringing
1
All-off
1
0
All-off
0
Talk
0
Break-Before-Make Ringing to Talk Transition Logic Sequence
Ringing
T_SD
Timing
Break Return
Switches Switch
(SW3)
Z
-
Off
On
Hold this state for one-half of the ringing cycle.
0 ^{SW4 waiting for zero current to turn off.}
Off
Off
Zero current has occurred. SW4 has opened
Off
Off
Z
Close break switches
On
Off
Ringing
Switch
(SW4)
On
On
Off
Off
Logic states and explanations are provided in the “Truth Table” on page 9.
2.4 Data Latch
The CPC7591 has an integrated transparent data
latch. The latch enable operation is controlled by TTL
logic input levels at the LATCH pin. Data input to the
latch is via the input pin IN_RINGING, while the output of
the data latch are internal nodes used for state control.
When the LATCH enable control pin is at logic 0 the
data latch is transparent and the IN_RINGING input data
control signal flows directly through the data latch to
the state control circuitry. A change in IN_RINGING input
will be reflected by a change in switch state.
12
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