CPC7695 Datasheet, PDF (20/25 Pages) Clare, Inc. – Line Card Access Switch

INTEGRATED CIRCUITS DIVISION
CPC7695
2.7.3 Alternate Break-Before-Make Operation
The second break-before-make method is also
available for use with all versions of the CPC7695. As
shown in “Truth Table for CPC7695xA and CPC7695xB” on
page 15 and “Truth Table for CPC7695xC” on page 15,
when pulled to a logic low the bidirectional T_SD
interface disables all of the CPC7695 switches.
Although logically disabled, an active (closed) ringing
switch (SW4) will remain closed until the next current
zero crossing event.
As shown in the table “Operation Logic Table (Ringing to
Talk Transition): Break-Before-Make” on page 19, this
operation is similar to the one shown in “Alternate
Operation Logic Table (Ringing to Talk Transition):
Break-Before-Make” on page 20, except in the method
used to select the All-Off state and when the
IN_RINGING, IN_TESTin and IN_TESTout inputs are
reconfigured for theTalk 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,
IN_TESTin and IN_TESTout inputs to theTalk state
(0,0,0).
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 inputs while
forcing an All-Off state, and “Z,” which allows switch
control via the logic input pins. This requires the use of
an open-collector or open-drain type buffer.
Alternate Operation Logic Table (Ringing to Talk Transition): Break-Before-Make
State IN_RINGING IN_TESTin IN_TESTout Latch T_SD
Timing
Break
Switches
Ringing
Return
Switch
(SW3)
Ringing
Switch
(SW4)
Test
Switches
Ringing 1
0
0
0
Z
-
Off
On
On
Off
Hold this state for at least
All-Off
1
0
1
one-half of ringing cycle. SW4 Off
Off
On
Off
waiting for zero current to turn off.
X
0
Break-
Before- 0
0
0
Make
Zero current has occurred. SW4
has opened
Off
Off
Off
Off
Talk
0
0
0
0
Z
Break switches close.
On
Off
Off
Off
* For the CPC7695xA/B versions the input pattern (1,1,1) may also be used for the All-Off state.
2.8 Ringing Switch Zero-Cross Current Turn Off
After the application of a logic input to turn SW4 off,
the ringing switch is designed to delay the change in
state until the next zero-crossing. Once active, the
switch requires a zero-current crossing to turn off, and
therefore should not be used to switch a pure DC
signal. The switch will remain in the on state no matter
the logic input until the next zero crossing. These
switching characteristics will reduce and possibly
eliminate overall system impulse noise normally
associated with ringing switches. See IXYS Integrated
Circuits Division application note AN-144, Impulse Noise
Benefits of Line Card Access Switches for more
information. The attributes of ringing switch SW4 may
make it possible to eliminate the need for a zero-cross
switching scheme. A minimum impedance of 300 in
series with the ringing generator is recommended.
2.9 Power Supplies
Both a +5V supply and battery voltage are connected
to the CPC7695. Switch state control is powered
exclusively by the +5V supply. As a result, the
CPC7695 exhibits extremely low power consumption
during active and idle states.
20
www.ixysic.com
R01